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- /*
- * Read-Copy Update mechanism for mutual exclusion
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
- * Copyright IBM Corporation, 2008
- *
- * Authors: Dipankar Sarma <dipankar@in.ibm.com>
- * Manfred Spraul <manfred@colorfullife.com>
- * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
- *
- * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
- * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
- *
- * For detailed explanation of Read-Copy Update mechanism see -
- * Documentation/RCU
- */
- #define pr_fmt(fmt) "rcu: " fmt
- #include <linux/types.h>
- #include <linux/kernel.h>
- #include <linux/init.h>
- #include <linux/spinlock.h>
- #include <linux/smp.h>
- #include <linux/rcupdate_wait.h>
- #include <linux/interrupt.h>
- #include <linux/sched.h>
- #include <linux/sched/debug.h>
- #include <linux/nmi.h>
- #include <linux/atomic.h>
- #include <linux/bitops.h>
- #include <linux/export.h>
- #include <linux/completion.h>
- #include <linux/moduleparam.h>
- #include <linux/percpu.h>
- #include <linux/notifier.h>
- #include <linux/cpu.h>
- #include <linux/mutex.h>
- #include <linux/time.h>
- #include <linux/kernel_stat.h>
- #include <linux/wait.h>
- #include <linux/kthread.h>
- #include <uapi/linux/sched/types.h>
- #include <linux/prefetch.h>
- #include <linux/delay.h>
- #include <linux/stop_machine.h>
- #include <linux/random.h>
- #include <linux/trace_events.h>
- #include <linux/suspend.h>
- #include <linux/ftrace.h>
- #include "tree.h"
- #include "rcu.h"
- #ifdef MODULE_PARAM_PREFIX
- #undef MODULE_PARAM_PREFIX
- #endif
- #define MODULE_PARAM_PREFIX "rcutree."
- /* Data structures. */
- /*
- * In order to export the rcu_state name to the tracing tools, it
- * needs to be added in the __tracepoint_string section.
- * This requires defining a separate variable tp_<sname>_varname
- * that points to the string being used, and this will allow
- * the tracing userspace tools to be able to decipher the string
- * address to the matching string.
- */
- #ifdef CONFIG_TRACING
- # define DEFINE_RCU_TPS(sname) \
- static char sname##_varname[] = #sname; \
- static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
- # define RCU_STATE_NAME(sname) sname##_varname
- #else
- # define DEFINE_RCU_TPS(sname)
- # define RCU_STATE_NAME(sname) __stringify(sname)
- #endif
- #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
- DEFINE_RCU_TPS(sname) \
- static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
- struct rcu_state sname##_state = { \
- .level = { &sname##_state.node[0] }, \
- .rda = &sname##_data, \
- .call = cr, \
- .gp_state = RCU_GP_IDLE, \
- .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT, \
- .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
- .name = RCU_STATE_NAME(sname), \
- .abbr = sabbr, \
- .exp_mutex = __MUTEX_INITIALIZER(sname##_state.exp_mutex), \
- .exp_wake_mutex = __MUTEX_INITIALIZER(sname##_state.exp_wake_mutex), \
- .ofl_lock = __SPIN_LOCK_UNLOCKED(sname##_state.ofl_lock), \
- }
- RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
- RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
- static struct rcu_state *const rcu_state_p;
- LIST_HEAD(rcu_struct_flavors);
- /* Dump rcu_node combining tree at boot to verify correct setup. */
- static bool dump_tree;
- module_param(dump_tree, bool, 0444);
- /* Control rcu_node-tree auto-balancing at boot time. */
- static bool rcu_fanout_exact;
- module_param(rcu_fanout_exact, bool, 0444);
- /* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
- static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
- module_param(rcu_fanout_leaf, int, 0444);
- int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
- /* Number of rcu_nodes at specified level. */
- int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
- int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
- /* panic() on RCU Stall sysctl. */
- int sysctl_panic_on_rcu_stall __read_mostly;
- /*
- * The rcu_scheduler_active variable is initialized to the value
- * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
- * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
- * RCU can assume that there is but one task, allowing RCU to (for example)
- * optimize synchronize_rcu() to a simple barrier(). When this variable
- * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
- * to detect real grace periods. This variable is also used to suppress
- * boot-time false positives from lockdep-RCU error checking. Finally, it
- * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
- * is fully initialized, including all of its kthreads having been spawned.
- */
- int rcu_scheduler_active __read_mostly;
- EXPORT_SYMBOL_GPL(rcu_scheduler_active);
- /*
- * The rcu_scheduler_fully_active variable transitions from zero to one
- * during the early_initcall() processing, which is after the scheduler
- * is capable of creating new tasks. So RCU processing (for example,
- * creating tasks for RCU priority boosting) must be delayed until after
- * rcu_scheduler_fully_active transitions from zero to one. We also
- * currently delay invocation of any RCU callbacks until after this point.
- *
- * It might later prove better for people registering RCU callbacks during
- * early boot to take responsibility for these callbacks, but one step at
- * a time.
- */
- static int rcu_scheduler_fully_active __read_mostly;
- static void
- rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
- struct rcu_node *rnp, unsigned long gps, unsigned long flags);
- static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
- static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
- static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
- static void invoke_rcu_core(void);
- static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
- static void rcu_report_exp_rdp(struct rcu_state *rsp,
- struct rcu_data *rdp, bool wake);
- static void sync_sched_exp_online_cleanup(int cpu);
- /* rcuc/rcub kthread realtime priority */
- static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
- module_param(kthread_prio, int, 0644);
- /* Delay in jiffies for grace-period initialization delays, debug only. */
- static int gp_preinit_delay;
- module_param(gp_preinit_delay, int, 0444);
- static int gp_init_delay;
- module_param(gp_init_delay, int, 0444);
- static int gp_cleanup_delay;
- module_param(gp_cleanup_delay, int, 0444);
- /* Retreive RCU kthreads priority for rcutorture */
- int rcu_get_gp_kthreads_prio(void)
- {
- return kthread_prio;
- }
- EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
- /*
- * Number of grace periods between delays, normalized by the duration of
- * the delay. The longer the delay, the more the grace periods between
- * each delay. The reason for this normalization is that it means that,
- * for non-zero delays, the overall slowdown of grace periods is constant
- * regardless of the duration of the delay. This arrangement balances
- * the need for long delays to increase some race probabilities with the
- * need for fast grace periods to increase other race probabilities.
- */
- #define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */
- /*
- * Compute the mask of online CPUs for the specified rcu_node structure.
- * This will not be stable unless the rcu_node structure's ->lock is
- * held, but the bit corresponding to the current CPU will be stable
- * in most contexts.
- */
- unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
- {
- return READ_ONCE(rnp->qsmaskinitnext);
- }
- /*
- * Return true if an RCU grace period is in progress. The READ_ONCE()s
- * permit this function to be invoked without holding the root rcu_node
- * structure's ->lock, but of course results can be subject to change.
- */
- static int rcu_gp_in_progress(struct rcu_state *rsp)
- {
- return rcu_seq_state(rcu_seq_current(&rsp->gp_seq));
- }
- /*
- * Note a quiescent state. Because we do not need to know
- * how many quiescent states passed, just if there was at least
- * one since the start of the grace period, this just sets a flag.
- * The caller must have disabled preemption.
- */
- void rcu_sched_qs(void)
- {
- RCU_LOCKDEP_WARN(preemptible(), "rcu_sched_qs() invoked with preemption enabled!!!");
- if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
- return;
- trace_rcu_grace_period(TPS("rcu_sched"),
- __this_cpu_read(rcu_sched_data.gp_seq),
- TPS("cpuqs"));
- __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
- if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
- return;
- __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
- rcu_report_exp_rdp(&rcu_sched_state,
- this_cpu_ptr(&rcu_sched_data), true);
- }
- void rcu_bh_qs(void)
- {
- RCU_LOCKDEP_WARN(preemptible(), "rcu_bh_qs() invoked with preemption enabled!!!");
- if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
- trace_rcu_grace_period(TPS("rcu_bh"),
- __this_cpu_read(rcu_bh_data.gp_seq),
- TPS("cpuqs"));
- __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
- }
- }
- /*
- * Steal a bit from the bottom of ->dynticks for idle entry/exit
- * control. Initially this is for TLB flushing.
- */
- #define RCU_DYNTICK_CTRL_MASK 0x1
- #define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
- #ifndef rcu_eqs_special_exit
- #define rcu_eqs_special_exit() do { } while (0)
- #endif
- static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
- .dynticks_nesting = 1,
- .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
- .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
- };
- /*
- * Record entry into an extended quiescent state. This is only to be
- * called when not already in an extended quiescent state.
- */
- static void rcu_dynticks_eqs_enter(void)
- {
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
- int seq;
- /*
- * CPUs seeing atomic_add_return() must see prior RCU read-side
- * critical sections, and we also must force ordering with the
- * next idle sojourn.
- */
- seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
- /* Better be in an extended quiescent state! */
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
- (seq & RCU_DYNTICK_CTRL_CTR));
- /* Better not have special action (TLB flush) pending! */
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
- (seq & RCU_DYNTICK_CTRL_MASK));
- }
- /*
- * Record exit from an extended quiescent state. This is only to be
- * called from an extended quiescent state.
- */
- static void rcu_dynticks_eqs_exit(void)
- {
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
- int seq;
- /*
- * CPUs seeing atomic_add_return() must see prior idle sojourns,
- * and we also must force ordering with the next RCU read-side
- * critical section.
- */
- seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
- !(seq & RCU_DYNTICK_CTRL_CTR));
- if (seq & RCU_DYNTICK_CTRL_MASK) {
- atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdtp->dynticks);
- smp_mb__after_atomic(); /* _exit after clearing mask. */
- /* Prefer duplicate flushes to losing a flush. */
- rcu_eqs_special_exit();
- }
- }
- /*
- * Reset the current CPU's ->dynticks counter to indicate that the
- * newly onlined CPU is no longer in an extended quiescent state.
- * This will either leave the counter unchanged, or increment it
- * to the next non-quiescent value.
- *
- * The non-atomic test/increment sequence works because the upper bits
- * of the ->dynticks counter are manipulated only by the corresponding CPU,
- * or when the corresponding CPU is offline.
- */
- static void rcu_dynticks_eqs_online(void)
- {
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
- if (atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR)
- return;
- atomic_add(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
- }
- /*
- * Is the current CPU in an extended quiescent state?
- *
- * No ordering, as we are sampling CPU-local information.
- */
- bool rcu_dynticks_curr_cpu_in_eqs(void)
- {
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
- return !(atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR);
- }
- /*
- * Snapshot the ->dynticks counter with full ordering so as to allow
- * stable comparison of this counter with past and future snapshots.
- */
- int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
- {
- int snap = atomic_add_return(0, &rdtp->dynticks);
- return snap & ~RCU_DYNTICK_CTRL_MASK;
- }
- /*
- * Return true if the snapshot returned from rcu_dynticks_snap()
- * indicates that RCU is in an extended quiescent state.
- */
- static bool rcu_dynticks_in_eqs(int snap)
- {
- return !(snap & RCU_DYNTICK_CTRL_CTR);
- }
- /*
- * Return true if the CPU corresponding to the specified rcu_dynticks
- * structure has spent some time in an extended quiescent state since
- * rcu_dynticks_snap() returned the specified snapshot.
- */
- static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)
- {
- return snap != rcu_dynticks_snap(rdtp);
- }
- /*
- * Set the special (bottom) bit of the specified CPU so that it
- * will take special action (such as flushing its TLB) on the
- * next exit from an extended quiescent state. Returns true if
- * the bit was successfully set, or false if the CPU was not in
- * an extended quiescent state.
- */
- bool rcu_eqs_special_set(int cpu)
- {
- int old;
- int new;
- struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
- do {
- old = atomic_read(&rdtp->dynticks);
- if (old & RCU_DYNTICK_CTRL_CTR)
- return false;
- new = old | RCU_DYNTICK_CTRL_MASK;
- } while (atomic_cmpxchg(&rdtp->dynticks, old, new) != old);
- return true;
- }
- /*
- * Let the RCU core know that this CPU has gone through the scheduler,
- * which is a quiescent state. This is called when the need for a
- * quiescent state is urgent, so we burn an atomic operation and full
- * memory barriers to let the RCU core know about it, regardless of what
- * this CPU might (or might not) do in the near future.
- *
- * We inform the RCU core by emulating a zero-duration dyntick-idle period.
- *
- * The caller must have disabled interrupts and must not be idle.
- */
- static void rcu_momentary_dyntick_idle(void)
- {
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
- int special;
- raw_cpu_write(rcu_dynticks.rcu_need_heavy_qs, false);
- special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
- /* It is illegal to call this from idle state. */
- WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
- }
- /*
- * Note a context switch. This is a quiescent state for RCU-sched,
- * and requires special handling for preemptible RCU.
- * The caller must have disabled interrupts.
- */
- void rcu_note_context_switch(bool preempt)
- {
- barrier(); /* Avoid RCU read-side critical sections leaking down. */
- trace_rcu_utilization(TPS("Start context switch"));
- rcu_sched_qs();
- rcu_preempt_note_context_switch(preempt);
- /* Load rcu_urgent_qs before other flags. */
- if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs)))
- goto out;
- this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
- if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs)))
- rcu_momentary_dyntick_idle();
- this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
- if (!preempt)
- rcu_tasks_qs(current);
- out:
- trace_rcu_utilization(TPS("End context switch"));
- barrier(); /* Avoid RCU read-side critical sections leaking up. */
- }
- EXPORT_SYMBOL_GPL(rcu_note_context_switch);
- /*
- * Register a quiescent state for all RCU flavors. If there is an
- * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
- * dyntick-idle quiescent state visible to other CPUs (but only for those
- * RCU flavors in desperate need of a quiescent state, which will normally
- * be none of them). Either way, do a lightweight quiescent state for
- * all RCU flavors.
- *
- * The barrier() calls are redundant in the common case when this is
- * called externally, but just in case this is called from within this
- * file.
- *
- */
- void rcu_all_qs(void)
- {
- unsigned long flags;
- if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
- return;
- preempt_disable();
- /* Load rcu_urgent_qs before other flags. */
- if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
- preempt_enable();
- return;
- }
- this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
- barrier(); /* Avoid RCU read-side critical sections leaking down. */
- if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
- local_irq_save(flags);
- rcu_momentary_dyntick_idle();
- local_irq_restore(flags);
- }
- if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)))
- rcu_sched_qs();
- this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
- barrier(); /* Avoid RCU read-side critical sections leaking up. */
- preempt_enable();
- }
- EXPORT_SYMBOL_GPL(rcu_all_qs);
- #define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch. */
- static long blimit = DEFAULT_RCU_BLIMIT;
- #define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */
- static long qhimark = DEFAULT_RCU_QHIMARK;
- #define DEFAULT_RCU_QLOMARK 100 /* Once only this many pending, use blimit. */
- static long qlowmark = DEFAULT_RCU_QLOMARK;
- module_param(blimit, long, 0444);
- module_param(qhimark, long, 0444);
- module_param(qlowmark, long, 0444);
- static ulong jiffies_till_first_fqs = ULONG_MAX;
- static ulong jiffies_till_next_fqs = ULONG_MAX;
- static bool rcu_kick_kthreads;
- static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
- {
- ulong j;
- int ret = kstrtoul(val, 0, &j);
- if (!ret)
- WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
- return ret;
- }
- static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
- {
- ulong j;
- int ret = kstrtoul(val, 0, &j);
- if (!ret)
- WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
- return ret;
- }
- static struct kernel_param_ops first_fqs_jiffies_ops = {
- .set = param_set_first_fqs_jiffies,
- .get = param_get_ulong,
- };
- static struct kernel_param_ops next_fqs_jiffies_ops = {
- .set = param_set_next_fqs_jiffies,
- .get = param_get_ulong,
- };
- module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
- module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
- module_param(rcu_kick_kthreads, bool, 0644);
- /*
- * How long the grace period must be before we start recruiting
- * quiescent-state help from rcu_note_context_switch().
- */
- static ulong jiffies_till_sched_qs = HZ / 10;
- module_param(jiffies_till_sched_qs, ulong, 0444);
- static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp));
- static void force_quiescent_state(struct rcu_state *rsp);
- static int rcu_pending(void);
- /*
- * Return the number of RCU GPs completed thus far for debug & stats.
- */
- unsigned long rcu_get_gp_seq(void)
- {
- return READ_ONCE(rcu_state_p->gp_seq);
- }
- EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
- /*
- * Return the number of RCU-sched GPs completed thus far for debug & stats.
- */
- unsigned long rcu_sched_get_gp_seq(void)
- {
- return READ_ONCE(rcu_sched_state.gp_seq);
- }
- EXPORT_SYMBOL_GPL(rcu_sched_get_gp_seq);
- /*
- * Return the number of RCU-bh GPs completed thus far for debug & stats.
- */
- unsigned long rcu_bh_get_gp_seq(void)
- {
- return READ_ONCE(rcu_bh_state.gp_seq);
- }
- EXPORT_SYMBOL_GPL(rcu_bh_get_gp_seq);
- /*
- * Return the number of RCU expedited batches completed thus far for
- * debug & stats. Odd numbers mean that a batch is in progress, even
- * numbers mean idle. The value returned will thus be roughly double
- * the cumulative batches since boot.
- */
- unsigned long rcu_exp_batches_completed(void)
- {
- return rcu_state_p->expedited_sequence;
- }
- EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
- /*
- * Return the number of RCU-sched expedited batches completed thus far
- * for debug & stats. Similar to rcu_exp_batches_completed().
- */
- unsigned long rcu_exp_batches_completed_sched(void)
- {
- return rcu_sched_state.expedited_sequence;
- }
- EXPORT_SYMBOL_GPL(rcu_exp_batches_completed_sched);
- /*
- * Force a quiescent state.
- */
- void rcu_force_quiescent_state(void)
- {
- force_quiescent_state(rcu_state_p);
- }
- EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
- /*
- * Force a quiescent state for RCU BH.
- */
- void rcu_bh_force_quiescent_state(void)
- {
- force_quiescent_state(&rcu_bh_state);
- }
- EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
- /*
- * Force a quiescent state for RCU-sched.
- */
- void rcu_sched_force_quiescent_state(void)
- {
- force_quiescent_state(&rcu_sched_state);
- }
- EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
- /*
- * Show the state of the grace-period kthreads.
- */
- void show_rcu_gp_kthreads(void)
- {
- int cpu;
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp) {
- pr_info("%s: wait state: %d ->state: %#lx\n",
- rsp->name, rsp->gp_state, rsp->gp_kthread->state);
- rcu_for_each_node_breadth_first(rsp, rnp) {
- if (ULONG_CMP_GE(rsp->gp_seq, rnp->gp_seq_needed))
- continue;
- pr_info("\trcu_node %d:%d ->gp_seq %lu ->gp_seq_needed %lu\n",
- rnp->grplo, rnp->grphi, rnp->gp_seq,
- rnp->gp_seq_needed);
- if (!rcu_is_leaf_node(rnp))
- continue;
- for_each_leaf_node_possible_cpu(rnp, cpu) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
- if (rdp->gpwrap ||
- ULONG_CMP_GE(rsp->gp_seq,
- rdp->gp_seq_needed))
- continue;
- pr_info("\tcpu %d ->gp_seq_needed %lu\n",
- cpu, rdp->gp_seq_needed);
- }
- }
- /* sched_show_task(rsp->gp_kthread); */
- }
- }
- EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
- /*
- * Send along grace-period-related data for rcutorture diagnostics.
- */
- void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
- unsigned long *gp_seq)
- {
- struct rcu_state *rsp = NULL;
- switch (test_type) {
- case RCU_FLAVOR:
- rsp = rcu_state_p;
- break;
- case RCU_BH_FLAVOR:
- rsp = &rcu_bh_state;
- break;
- case RCU_SCHED_FLAVOR:
- rsp = &rcu_sched_state;
- break;
- default:
- break;
- }
- if (rsp == NULL)
- return;
- *flags = READ_ONCE(rsp->gp_flags);
- *gp_seq = rcu_seq_current(&rsp->gp_seq);
- }
- EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
- /*
- * Return the root node of the specified rcu_state structure.
- */
- static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
- {
- return &rsp->node[0];
- }
- /*
- * Enter an RCU extended quiescent state, which can be either the
- * idle loop or adaptive-tickless usermode execution.
- *
- * We crowbar the ->dynticks_nmi_nesting field to zero to allow for
- * the possibility of usermode upcalls having messed up our count
- * of interrupt nesting level during the prior busy period.
- */
- static void rcu_eqs_enter(bool user)
- {
- struct rcu_state *rsp;
- struct rcu_data *rdp;
- struct rcu_dynticks *rdtp;
- rdtp = this_cpu_ptr(&rcu_dynticks);
- WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0);
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
- rdtp->dynticks_nesting == 0);
- if (rdtp->dynticks_nesting != 1) {
- rdtp->dynticks_nesting--;
- return;
- }
- lockdep_assert_irqs_disabled();
- trace_rcu_dyntick(TPS("Start"), rdtp->dynticks_nesting, 0, rdtp->dynticks);
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
- for_each_rcu_flavor(rsp) {
- rdp = this_cpu_ptr(rsp->rda);
- do_nocb_deferred_wakeup(rdp);
- }
- rcu_prepare_for_idle();
- WRITE_ONCE(rdtp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
- rcu_dynticks_eqs_enter();
- rcu_dynticks_task_enter();
- }
- /**
- * rcu_idle_enter - inform RCU that current CPU is entering idle
- *
- * Enter idle mode, in other words, -leave- the mode in which RCU
- * read-side critical sections can occur. (Though RCU read-side
- * critical sections can occur in irq handlers in idle, a possibility
- * handled by irq_enter() and irq_exit().)
- *
- * If you add or remove a call to rcu_idle_enter(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_idle_enter(void)
- {
- lockdep_assert_irqs_disabled();
- rcu_eqs_enter(false);
- }
- #ifdef CONFIG_NO_HZ_FULL
- /**
- * rcu_user_enter - inform RCU that we are resuming userspace.
- *
- * Enter RCU idle mode right before resuming userspace. No use of RCU
- * is permitted between this call and rcu_user_exit(). This way the
- * CPU doesn't need to maintain the tick for RCU maintenance purposes
- * when the CPU runs in userspace.
- *
- * If you add or remove a call to rcu_user_enter(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_user_enter(void)
- {
- lockdep_assert_irqs_disabled();
- rcu_eqs_enter(true);
- }
- #endif /* CONFIG_NO_HZ_FULL */
- /**
- * rcu_nmi_exit - inform RCU of exit from NMI context
- *
- * If we are returning from the outermost NMI handler that interrupted an
- * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
- * to let the RCU grace-period handling know that the CPU is back to
- * being RCU-idle.
- *
- * If you add or remove a call to rcu_nmi_exit(), be sure to test
- * with CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_nmi_exit(void)
- {
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
- /*
- * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
- * (We are exiting an NMI handler, so RCU better be paying attention
- * to us!)
- */
- WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
- WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
- /*
- * If the nesting level is not 1, the CPU wasn't RCU-idle, so
- * leave it in non-RCU-idle state.
- */
- if (rdtp->dynticks_nmi_nesting != 1) {
- trace_rcu_dyntick(TPS("--="), rdtp->dynticks_nmi_nesting, rdtp->dynticks_nmi_nesting - 2, rdtp->dynticks);
- WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* No store tearing. */
- rdtp->dynticks_nmi_nesting - 2);
- return;
- }
- /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
- trace_rcu_dyntick(TPS("Startirq"), rdtp->dynticks_nmi_nesting, 0, rdtp->dynticks);
- WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
- rcu_dynticks_eqs_enter();
- }
- /**
- * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
- *
- * Exit from an interrupt handler, which might possibly result in entering
- * idle mode, in other words, leaving the mode in which read-side critical
- * sections can occur. The caller must have disabled interrupts.
- *
- * This code assumes that the idle loop never does anything that might
- * result in unbalanced calls to irq_enter() and irq_exit(). If your
- * architecture's idle loop violates this assumption, RCU will give you what
- * you deserve, good and hard. But very infrequently and irreproducibly.
- *
- * Use things like work queues to work around this limitation.
- *
- * You have been warned.
- *
- * If you add or remove a call to rcu_irq_exit(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_irq_exit(void)
- {
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
- lockdep_assert_irqs_disabled();
- if (rdtp->dynticks_nmi_nesting == 1)
- rcu_prepare_for_idle();
- rcu_nmi_exit();
- if (rdtp->dynticks_nmi_nesting == 0)
- rcu_dynticks_task_enter();
- }
- /*
- * Wrapper for rcu_irq_exit() where interrupts are enabled.
- *
- * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
- * with CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_irq_exit_irqson(void)
- {
- unsigned long flags;
- local_irq_save(flags);
- rcu_irq_exit();
- local_irq_restore(flags);
- }
- /*
- * Exit an RCU extended quiescent state, which can be either the
- * idle loop or adaptive-tickless usermode execution.
- *
- * We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
- * allow for the possibility of usermode upcalls messing up our count of
- * interrupt nesting level during the busy period that is just now starting.
- */
- static void rcu_eqs_exit(bool user)
- {
- struct rcu_dynticks *rdtp;
- long oldval;
- lockdep_assert_irqs_disabled();
- rdtp = this_cpu_ptr(&rcu_dynticks);
- oldval = rdtp->dynticks_nesting;
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
- if (oldval) {
- rdtp->dynticks_nesting++;
- return;
- }
- rcu_dynticks_task_exit();
- rcu_dynticks_eqs_exit();
- rcu_cleanup_after_idle();
- trace_rcu_dyntick(TPS("End"), rdtp->dynticks_nesting, 1, rdtp->dynticks);
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
- WRITE_ONCE(rdtp->dynticks_nesting, 1);
- WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
- }
- /**
- * rcu_idle_exit - inform RCU that current CPU is leaving idle
- *
- * Exit idle mode, in other words, -enter- the mode in which RCU
- * read-side critical sections can occur.
- *
- * If you add or remove a call to rcu_idle_exit(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_idle_exit(void)
- {
- unsigned long flags;
- local_irq_save(flags);
- rcu_eqs_exit(false);
- local_irq_restore(flags);
- }
- #ifdef CONFIG_NO_HZ_FULL
- /**
- * rcu_user_exit - inform RCU that we are exiting userspace.
- *
- * Exit RCU idle mode while entering the kernel because it can
- * run a RCU read side critical section anytime.
- *
- * If you add or remove a call to rcu_user_exit(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_user_exit(void)
- {
- rcu_eqs_exit(1);
- }
- #endif /* CONFIG_NO_HZ_FULL */
- /**
- * rcu_nmi_enter - inform RCU of entry to NMI context
- *
- * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
- * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
- * that the CPU is active. This implementation permits nested NMIs, as
- * long as the nesting level does not overflow an int. (You will probably
- * run out of stack space first.)
- *
- * If you add or remove a call to rcu_nmi_enter(), be sure to test
- * with CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_nmi_enter(void)
- {
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
- long incby = 2;
- /* Complain about underflow. */
- WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
- /*
- * If idle from RCU viewpoint, atomically increment ->dynticks
- * to mark non-idle and increment ->dynticks_nmi_nesting by one.
- * Otherwise, increment ->dynticks_nmi_nesting by two. This means
- * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
- * to be in the outermost NMI handler that interrupted an RCU-idle
- * period (observation due to Andy Lutomirski).
- */
- if (rcu_dynticks_curr_cpu_in_eqs()) {
- rcu_dynticks_eqs_exit();
- incby = 1;
- }
- trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
- rdtp->dynticks_nmi_nesting,
- rdtp->dynticks_nmi_nesting + incby, rdtp->dynticks);
- WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* Prevent store tearing. */
- rdtp->dynticks_nmi_nesting + incby);
- barrier();
- }
- /**
- * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
- *
- * Enter an interrupt handler, which might possibly result in exiting
- * idle mode, in other words, entering the mode in which read-side critical
- * sections can occur. The caller must have disabled interrupts.
- *
- * Note that the Linux kernel is fully capable of entering an interrupt
- * handler that it never exits, for example when doing upcalls to user mode!
- * This code assumes that the idle loop never does upcalls to user mode.
- * If your architecture's idle loop does do upcalls to user mode (or does
- * anything else that results in unbalanced calls to the irq_enter() and
- * irq_exit() functions), RCU will give you what you deserve, good and hard.
- * But very infrequently and irreproducibly.
- *
- * Use things like work queues to work around this limitation.
- *
- * You have been warned.
- *
- * If you add or remove a call to rcu_irq_enter(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_irq_enter(void)
- {
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
- lockdep_assert_irqs_disabled();
- if (rdtp->dynticks_nmi_nesting == 0)
- rcu_dynticks_task_exit();
- rcu_nmi_enter();
- if (rdtp->dynticks_nmi_nesting == 1)
- rcu_cleanup_after_idle();
- }
- /*
- * Wrapper for rcu_irq_enter() where interrupts are enabled.
- *
- * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
- * with CONFIG_RCU_EQS_DEBUG=y.
- */
- void rcu_irq_enter_irqson(void)
- {
- unsigned long flags;
- local_irq_save(flags);
- rcu_irq_enter();
- local_irq_restore(flags);
- }
- /**
- * rcu_is_watching - see if RCU thinks that the current CPU is idle
- *
- * Return true if RCU is watching the running CPU, which means that this
- * CPU can safely enter RCU read-side critical sections. In other words,
- * if the current CPU is in its idle loop and is neither in an interrupt
- * or NMI handler, return true.
- */
- bool notrace rcu_is_watching(void)
- {
- bool ret;
- preempt_disable_notrace();
- ret = !rcu_dynticks_curr_cpu_in_eqs();
- preempt_enable_notrace();
- return ret;
- }
- EXPORT_SYMBOL_GPL(rcu_is_watching);
- /*
- * If a holdout task is actually running, request an urgent quiescent
- * state from its CPU. This is unsynchronized, so migrations can cause
- * the request to go to the wrong CPU. Which is OK, all that will happen
- * is that the CPU's next context switch will be a bit slower and next
- * time around this task will generate another request.
- */
- void rcu_request_urgent_qs_task(struct task_struct *t)
- {
- int cpu;
- barrier();
- cpu = task_cpu(t);
- if (!task_curr(t))
- return; /* This task is not running on that CPU. */
- smp_store_release(per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, cpu), true);
- }
- #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
- /*
- * Is the current CPU online as far as RCU is concerned?
- *
- * Disable preemption to avoid false positives that could otherwise
- * happen due to the current CPU number being sampled, this task being
- * preempted, its old CPU being taken offline, resuming on some other CPU,
- * then determining that its old CPU is now offline. Because there are
- * multiple flavors of RCU, and because this function can be called in the
- * midst of updating the flavors while a given CPU coming online or going
- * offline, it is necessary to check all flavors. If any of the flavors
- * believe that given CPU is online, it is considered to be online.
- *
- * Disable checking if in an NMI handler because we cannot safely
- * report errors from NMI handlers anyway. In addition, it is OK to use
- * RCU on an offline processor during initial boot, hence the check for
- * rcu_scheduler_fully_active.
- */
- bool rcu_lockdep_current_cpu_online(void)
- {
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- struct rcu_state *rsp;
- if (in_nmi() || !rcu_scheduler_fully_active)
- return true;
- preempt_disable();
- for_each_rcu_flavor(rsp) {
- rdp = this_cpu_ptr(rsp->rda);
- rnp = rdp->mynode;
- if (rdp->grpmask & rcu_rnp_online_cpus(rnp)) {
- preempt_enable();
- return true;
- }
- }
- preempt_enable();
- return false;
- }
- EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
- #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
- /**
- * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
- *
- * If the current CPU is idle or running at a first-level (not nested)
- * interrupt from idle, return true. The caller must have at least
- * disabled preemption.
- */
- static int rcu_is_cpu_rrupt_from_idle(void)
- {
- return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 0 &&
- __this_cpu_read(rcu_dynticks.dynticks_nmi_nesting) <= 1;
- }
- /*
- * We are reporting a quiescent state on behalf of some other CPU, so
- * it is our responsibility to check for and handle potential overflow
- * of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
- * After all, the CPU might be in deep idle state, and thus executing no
- * code whatsoever.
- */
- static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
- {
- raw_lockdep_assert_held_rcu_node(rnp);
- if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
- rnp->gp_seq))
- WRITE_ONCE(rdp->gpwrap, true);
- if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
- rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
- }
- /*
- * Snapshot the specified CPU's dynticks counter so that we can later
- * credit them with an implicit quiescent state. Return 1 if this CPU
- * is in dynticks idle mode, which is an extended quiescent state.
- */
- static int dyntick_save_progress_counter(struct rcu_data *rdp)
- {
- rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
- if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
- trace_rcu_fqs(rdp->rsp->name, rdp->gp_seq, rdp->cpu, TPS("dti"));
- rcu_gpnum_ovf(rdp->mynode, rdp);
- return 1;
- }
- return 0;
- }
- /*
- * Handler for the irq_work request posted when a grace period has
- * gone on for too long, but not yet long enough for an RCU CPU
- * stall warning. Set state appropriately, but just complain if
- * there is unexpected state on entry.
- */
- static void rcu_iw_handler(struct irq_work *iwp)
- {
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- rdp = container_of(iwp, struct rcu_data, rcu_iw);
- rnp = rdp->mynode;
- raw_spin_lock_rcu_node(rnp);
- if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
- rdp->rcu_iw_gp_seq = rnp->gp_seq;
- rdp->rcu_iw_pending = false;
- }
- raw_spin_unlock_rcu_node(rnp);
- }
- /*
- * Return true if the specified CPU has passed through a quiescent
- * state by virtue of being in or having passed through an dynticks
- * idle state since the last call to dyntick_save_progress_counter()
- * for this same CPU, or by virtue of having been offline.
- */
- static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
- {
- unsigned long jtsq;
- bool *rnhqp;
- bool *ruqp;
- struct rcu_node *rnp = rdp->mynode;
- /*
- * If the CPU passed through or entered a dynticks idle phase with
- * no active irq/NMI handlers, then we can safely pretend that the CPU
- * already acknowledged the request to pass through a quiescent
- * state. Either way, that CPU cannot possibly be in an RCU
- * read-side critical section that started before the beginning
- * of the current RCU grace period.
- */
- if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) {
- trace_rcu_fqs(rdp->rsp->name, rdp->gp_seq, rdp->cpu, TPS("dti"));
- rdp->dynticks_fqs++;
- rcu_gpnum_ovf(rnp, rdp);
- return 1;
- }
- /*
- * Has this CPU encountered a cond_resched() since the beginning
- * of the grace period? For this to be the case, the CPU has to
- * have noticed the current grace period. This might not be the
- * case for nohz_full CPUs looping in the kernel.
- */
- jtsq = jiffies_till_sched_qs;
- ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
- if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
- READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
- rcu_seq_current(&rdp->gp_seq) == rnp->gp_seq && !rdp->gpwrap) {
- trace_rcu_fqs(rdp->rsp->name, rdp->gp_seq, rdp->cpu, TPS("rqc"));
- rcu_gpnum_ovf(rnp, rdp);
- return 1;
- } else if (time_after(jiffies, rdp->rsp->gp_start + jtsq)) {
- /* Load rcu_qs_ctr before store to rcu_urgent_qs. */
- smp_store_release(ruqp, true);
- }
- /* If waiting too long on an offline CPU, complain. */
- if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp)) &&
- time_after(jiffies, rdp->rsp->gp_start + HZ)) {
- bool onl;
- struct rcu_node *rnp1;
- WARN_ON(1); /* Offline CPUs are supposed to report QS! */
- pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
- __func__, rnp->grplo, rnp->grphi, rnp->level,
- (long)rnp->gp_seq, (long)rnp->completedqs);
- for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
- pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
- __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
- onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
- pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
- __func__, rdp->cpu, ".o"[onl],
- (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
- (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
- return 1; /* Break things loose after complaining. */
- }
- /*
- * A CPU running for an extended time within the kernel can
- * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode,
- * even context-switching back and forth between a pair of
- * in-kernel CPU-bound tasks cannot advance grace periods.
- * So if the grace period is old enough, make the CPU pay attention.
- * Note that the unsynchronized assignments to the per-CPU
- * rcu_need_heavy_qs variable are safe. Yes, setting of
- * bits can be lost, but they will be set again on the next
- * force-quiescent-state pass. So lost bit sets do not result
- * in incorrect behavior, merely in a grace period lasting
- * a few jiffies longer than it might otherwise. Because
- * there are at most four threads involved, and because the
- * updates are only once every few jiffies, the probability of
- * lossage (and thus of slight grace-period extension) is
- * quite low.
- */
- rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu);
- if (!READ_ONCE(*rnhqp) &&
- (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
- time_after(jiffies, rdp->rsp->jiffies_resched))) {
- WRITE_ONCE(*rnhqp, true);
- /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
- smp_store_release(ruqp, true);
- rdp->rsp->jiffies_resched += jtsq; /* Re-enable beating. */
- }
- /*
- * If more than halfway to RCU CPU stall-warning time, do a
- * resched_cpu() to try to loosen things up a bit. Also check to
- * see if the CPU is getting hammered with interrupts, but only
- * once per grace period, just to keep the IPIs down to a dull roar.
- */
- if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2) {
- resched_cpu(rdp->cpu);
- if (IS_ENABLED(CONFIG_IRQ_WORK) &&
- !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
- (rnp->ffmask & rdp->grpmask)) {
- init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
- rdp->rcu_iw_pending = true;
- rdp->rcu_iw_gp_seq = rnp->gp_seq;
- irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
- }
- }
- return 0;
- }
- static void record_gp_stall_check_time(struct rcu_state *rsp)
- {
- unsigned long j = jiffies;
- unsigned long j1;
- rsp->gp_start = j;
- j1 = rcu_jiffies_till_stall_check();
- /* Record ->gp_start before ->jiffies_stall. */
- smp_store_release(&rsp->jiffies_stall, j + j1); /* ^^^ */
- rsp->jiffies_resched = j + j1 / 2;
- rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
- }
- /*
- * Convert a ->gp_state value to a character string.
- */
- static const char *gp_state_getname(short gs)
- {
- if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
- return "???";
- return gp_state_names[gs];
- }
- /*
- * Complain about starvation of grace-period kthread.
- */
- static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
- {
- unsigned long gpa;
- unsigned long j;
- j = jiffies;
- gpa = READ_ONCE(rsp->gp_activity);
- if (j - gpa > 2 * HZ) {
- pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
- rsp->name, j - gpa,
- (long)rcu_seq_current(&rsp->gp_seq),
- rsp->gp_flags,
- gp_state_getname(rsp->gp_state), rsp->gp_state,
- rsp->gp_kthread ? rsp->gp_kthread->state : ~0,
- rsp->gp_kthread ? task_cpu(rsp->gp_kthread) : -1);
- if (rsp->gp_kthread) {
- pr_err("RCU grace-period kthread stack dump:\n");
- sched_show_task(rsp->gp_kthread);
- wake_up_process(rsp->gp_kthread);
- }
- }
- }
- /*
- * Dump stacks of all tasks running on stalled CPUs. First try using
- * NMIs, but fall back to manual remote stack tracing on architectures
- * that don't support NMI-based stack dumps. The NMI-triggered stack
- * traces are more accurate because they are printed by the target CPU.
- */
- static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
- {
- int cpu;
- unsigned long flags;
- struct rcu_node *rnp;
- rcu_for_each_leaf_node(rsp, rnp) {
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- for_each_leaf_node_possible_cpu(rnp, cpu)
- if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
- if (!trigger_single_cpu_backtrace(cpu))
- dump_cpu_task(cpu);
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- }
- /*
- * If too much time has passed in the current grace period, and if
- * so configured, go kick the relevant kthreads.
- */
- static void rcu_stall_kick_kthreads(struct rcu_state *rsp)
- {
- unsigned long j;
- if (!rcu_kick_kthreads)
- return;
- j = READ_ONCE(rsp->jiffies_kick_kthreads);
- if (time_after(jiffies, j) && rsp->gp_kthread &&
- (rcu_gp_in_progress(rsp) || READ_ONCE(rsp->gp_flags))) {
- WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
- rcu_ftrace_dump(DUMP_ALL);
- wake_up_process(rsp->gp_kthread);
- WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ);
- }
- }
- static void panic_on_rcu_stall(void)
- {
- if (sysctl_panic_on_rcu_stall)
- panic("RCU Stall\n");
- }
- static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gp_seq)
- {
- int cpu;
- unsigned long flags;
- unsigned long gpa;
- unsigned long j;
- int ndetected = 0;
- struct rcu_node *rnp = rcu_get_root(rsp);
- long totqlen = 0;
- /* Kick and suppress, if so configured. */
- rcu_stall_kick_kthreads(rsp);
- if (rcu_cpu_stall_suppress)
- return;
- /*
- * OK, time to rat on our buddy...
- * See Documentation/RCU/stallwarn.txt for info on how to debug
- * RCU CPU stall warnings.
- */
- pr_err("INFO: %s detected stalls on CPUs/tasks:", rsp->name);
- print_cpu_stall_info_begin();
- rcu_for_each_leaf_node(rsp, rnp) {
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- ndetected += rcu_print_task_stall(rnp);
- if (rnp->qsmask != 0) {
- for_each_leaf_node_possible_cpu(rnp, cpu)
- if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
- print_cpu_stall_info(rsp, cpu);
- ndetected++;
- }
- }
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- print_cpu_stall_info_end();
- for_each_possible_cpu(cpu)
- totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
- cpu)->cblist);
- pr_cont("(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
- smp_processor_id(), (long)(jiffies - rsp->gp_start),
- (long)rcu_seq_current(&rsp->gp_seq), totqlen);
- if (ndetected) {
- rcu_dump_cpu_stacks(rsp);
- /* Complain about tasks blocking the grace period. */
- rcu_print_detail_task_stall(rsp);
- } else {
- if (rcu_seq_current(&rsp->gp_seq) != gp_seq) {
- pr_err("INFO: Stall ended before state dump start\n");
- } else {
- j = jiffies;
- gpa = READ_ONCE(rsp->gp_activity);
- pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
- rsp->name, j - gpa, j, gpa,
- jiffies_till_next_fqs,
- rcu_get_root(rsp)->qsmask);
- /* In this case, the current CPU might be at fault. */
- sched_show_task(current);
- }
- }
- /* Rewrite if needed in case of slow consoles. */
- if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
- WRITE_ONCE(rsp->jiffies_stall,
- jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
- rcu_check_gp_kthread_starvation(rsp);
- panic_on_rcu_stall();
- force_quiescent_state(rsp); /* Kick them all. */
- }
- static void print_cpu_stall(struct rcu_state *rsp)
- {
- int cpu;
- unsigned long flags;
- struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
- struct rcu_node *rnp = rcu_get_root(rsp);
- long totqlen = 0;
- /* Kick and suppress, if so configured. */
- rcu_stall_kick_kthreads(rsp);
- if (rcu_cpu_stall_suppress)
- return;
- /*
- * OK, time to rat on ourselves...
- * See Documentation/RCU/stallwarn.txt for info on how to debug
- * RCU CPU stall warnings.
- */
- pr_err("INFO: %s self-detected stall on CPU", rsp->name);
- print_cpu_stall_info_begin();
- raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
- print_cpu_stall_info(rsp, smp_processor_id());
- raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
- print_cpu_stall_info_end();
- for_each_possible_cpu(cpu)
- totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
- cpu)->cblist);
- pr_cont(" (t=%lu jiffies g=%ld q=%lu)\n",
- jiffies - rsp->gp_start,
- (long)rcu_seq_current(&rsp->gp_seq), totqlen);
- rcu_check_gp_kthread_starvation(rsp);
- rcu_dump_cpu_stacks(rsp);
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- /* Rewrite if needed in case of slow consoles. */
- if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
- WRITE_ONCE(rsp->jiffies_stall,
- jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- panic_on_rcu_stall();
- /*
- * Attempt to revive the RCU machinery by forcing a context switch.
- *
- * A context switch would normally allow the RCU state machine to make
- * progress and it could be we're stuck in kernel space without context
- * switches for an entirely unreasonable amount of time.
- */
- resched_cpu(smp_processor_id());
- }
- static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
- {
- unsigned long gs1;
- unsigned long gs2;
- unsigned long gps;
- unsigned long j;
- unsigned long jn;
- unsigned long js;
- struct rcu_node *rnp;
- if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
- !rcu_gp_in_progress(rsp))
- return;
- rcu_stall_kick_kthreads(rsp);
- j = jiffies;
- /*
- * Lots of memory barriers to reject false positives.
- *
- * The idea is to pick up rsp->gp_seq, then rsp->jiffies_stall,
- * then rsp->gp_start, and finally another copy of rsp->gp_seq.
- * These values are updated in the opposite order with memory
- * barriers (or equivalent) during grace-period initialization
- * and cleanup. Now, a false positive can occur if we get an new
- * value of rsp->gp_start and a old value of rsp->jiffies_stall.
- * But given the memory barriers, the only way that this can happen
- * is if one grace period ends and another starts between these
- * two fetches. This is detected by comparing the second fetch
- * of rsp->gp_seq with the previous fetch from rsp->gp_seq.
- *
- * Given this check, comparisons of jiffies, rsp->jiffies_stall,
- * and rsp->gp_start suffice to forestall false positives.
- */
- gs1 = READ_ONCE(rsp->gp_seq);
- smp_rmb(); /* Pick up ->gp_seq first... */
- js = READ_ONCE(rsp->jiffies_stall);
- smp_rmb(); /* ...then ->jiffies_stall before the rest... */
- gps = READ_ONCE(rsp->gp_start);
- smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
- gs2 = READ_ONCE(rsp->gp_seq);
- if (gs1 != gs2 ||
- ULONG_CMP_LT(j, js) ||
- ULONG_CMP_GE(gps, js))
- return; /* No stall or GP completed since entering function. */
- rnp = rdp->mynode;
- jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
- if (rcu_gp_in_progress(rsp) &&
- (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
- cmpxchg(&rsp->jiffies_stall, js, jn) == js) {
- /* We haven't checked in, so go dump stack. */
- print_cpu_stall(rsp);
- } else if (rcu_gp_in_progress(rsp) &&
- ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
- cmpxchg(&rsp->jiffies_stall, js, jn) == js) {
- /* They had a few time units to dump stack, so complain. */
- print_other_cpu_stall(rsp, gs2);
- }
- }
- /**
- * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
- *
- * Set the stall-warning timeout way off into the future, thus preventing
- * any RCU CPU stall-warning messages from appearing in the current set of
- * RCU grace periods.
- *
- * The caller must disable hard irqs.
- */
- void rcu_cpu_stall_reset(void)
- {
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp)
- WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
- }
- /* Trace-event wrapper function for trace_rcu_future_grace_period. */
- static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
- unsigned long gp_seq_req, const char *s)
- {
- trace_rcu_future_grace_period(rdp->rsp->name, rnp->gp_seq, gp_seq_req,
- rnp->level, rnp->grplo, rnp->grphi, s);
- }
- /*
- * rcu_start_this_gp - Request the start of a particular grace period
- * @rnp_start: The leaf node of the CPU from which to start.
- * @rdp: The rcu_data corresponding to the CPU from which to start.
- * @gp_seq_req: The gp_seq of the grace period to start.
- *
- * Start the specified grace period, as needed to handle newly arrived
- * callbacks. The required future grace periods are recorded in each
- * rcu_node structure's ->gp_seq_needed field. Returns true if there
- * is reason to awaken the grace-period kthread.
- *
- * The caller must hold the specified rcu_node structure's ->lock, which
- * is why the caller is responsible for waking the grace-period kthread.
- *
- * Returns true if the GP thread needs to be awakened else false.
- */
- static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
- unsigned long gp_seq_req)
- {
- bool ret = false;
- struct rcu_state *rsp = rdp->rsp;
- struct rcu_node *rnp;
- /*
- * Use funnel locking to either acquire the root rcu_node
- * structure's lock or bail out if the need for this grace period
- * has already been recorded -- or if that grace period has in
- * fact already started. If there is already a grace period in
- * progress in a non-leaf node, no recording is needed because the
- * end of the grace period will scan the leaf rcu_node structures.
- * Note that rnp_start->lock must not be released.
- */
- raw_lockdep_assert_held_rcu_node(rnp_start);
- trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
- for (rnp = rnp_start; 1; rnp = rnp->parent) {
- if (rnp != rnp_start)
- raw_spin_lock_rcu_node(rnp);
- if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
- rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
- (rnp != rnp_start &&
- rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
- trace_rcu_this_gp(rnp, rdp, gp_seq_req,
- TPS("Prestarted"));
- goto unlock_out;
- }
- rnp->gp_seq_needed = gp_seq_req;
- if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
- /*
- * We just marked the leaf or internal node, and a
- * grace period is in progress, which means that
- * rcu_gp_cleanup() will see the marking. Bail to
- * reduce contention.
- */
- trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
- TPS("Startedleaf"));
- goto unlock_out;
- }
- if (rnp != rnp_start && rnp->parent != NULL)
- raw_spin_unlock_rcu_node(rnp);
- if (!rnp->parent)
- break; /* At root, and perhaps also leaf. */
- }
- /* If GP already in progress, just leave, otherwise start one. */
- if (rcu_gp_in_progress(rsp)) {
- trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
- goto unlock_out;
- }
- trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
- WRITE_ONCE(rsp->gp_flags, rsp->gp_flags | RCU_GP_FLAG_INIT);
- rsp->gp_req_activity = jiffies;
- if (!rsp->gp_kthread) {
- trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
- goto unlock_out;
- }
- trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq), TPS("newreq"));
- ret = true; /* Caller must wake GP kthread. */
- unlock_out:
- /* Push furthest requested GP to leaf node and rcu_data structure. */
- if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
- rnp_start->gp_seq_needed = rnp->gp_seq_needed;
- rdp->gp_seq_needed = rnp->gp_seq_needed;
- }
- if (rnp != rnp_start)
- raw_spin_unlock_rcu_node(rnp);
- return ret;
- }
- /*
- * Clean up any old requests for the just-ended grace period. Also return
- * whether any additional grace periods have been requested.
- */
- static bool rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
- {
- bool needmore;
- struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
- needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
- if (!needmore)
- rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
- trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
- needmore ? TPS("CleanupMore") : TPS("Cleanup"));
- return needmore;
- }
- /*
- * Awaken the grace-period kthread. Don't do a self-awaken (unless in
- * an interrupt or softirq handler), and don't bother awakening when there
- * is nothing for the grace-period kthread to do (as in several CPUs raced
- * to awaken, and we lost), and finally don't try to awaken a kthread that
- * has not yet been created. If all those checks are passed, track some
- * debug information and awaken.
- *
- * So why do the self-wakeup when in an interrupt or softirq handler
- * in the grace-period kthread's context? Because the kthread might have
- * been interrupted just as it was going to sleep, and just after the final
- * pre-sleep check of the awaken condition. In this case, a wakeup really
- * is required, and is therefore supplied.
- */
- static void rcu_gp_kthread_wake(struct rcu_state *rsp)
- {
- if ((current == rsp->gp_kthread &&
- !in_interrupt() && !in_serving_softirq()) ||
- !READ_ONCE(rsp->gp_flags) ||
- !rsp->gp_kthread)
- return;
- swake_up_one(&rsp->gp_wq);
- }
- /*
- * If there is room, assign a ->gp_seq number to any callbacks on this
- * CPU that have not already been assigned. Also accelerate any callbacks
- * that were previously assigned a ->gp_seq number that has since proven
- * to be too conservative, which can happen if callbacks get assigned a
- * ->gp_seq number while RCU is idle, but with reference to a non-root
- * rcu_node structure. This function is idempotent, so it does not hurt
- * to call it repeatedly. Returns an flag saying that we should awaken
- * the RCU grace-period kthread.
- *
- * The caller must hold rnp->lock with interrupts disabled.
- */
- static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
- struct rcu_data *rdp)
- {
- unsigned long gp_seq_req;
- bool ret = false;
- raw_lockdep_assert_held_rcu_node(rnp);
- /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
- if (!rcu_segcblist_pend_cbs(&rdp->cblist))
- return false;
- /*
- * Callbacks are often registered with incomplete grace-period
- * information. Something about the fact that getting exact
- * information requires acquiring a global lock... RCU therefore
- * makes a conservative estimate of the grace period number at which
- * a given callback will become ready to invoke. The following
- * code checks this estimate and improves it when possible, thus
- * accelerating callback invocation to an earlier grace-period
- * number.
- */
- gp_seq_req = rcu_seq_snap(&rsp->gp_seq);
- if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
- ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
- /* Trace depending on how much we were able to accelerate. */
- if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
- trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("AccWaitCB"));
- else
- trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("AccReadyCB"));
- return ret;
- }
- /*
- * Similar to rcu_accelerate_cbs(), but does not require that the leaf
- * rcu_node structure's ->lock be held. It consults the cached value
- * of ->gp_seq_needed in the rcu_data structure, and if that indicates
- * that a new grace-period request be made, invokes rcu_accelerate_cbs()
- * while holding the leaf rcu_node structure's ->lock.
- */
- static void rcu_accelerate_cbs_unlocked(struct rcu_state *rsp,
- struct rcu_node *rnp,
- struct rcu_data *rdp)
- {
- unsigned long c;
- bool needwake;
- lockdep_assert_irqs_disabled();
- c = rcu_seq_snap(&rsp->gp_seq);
- if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
- /* Old request still live, so mark recent callbacks. */
- (void)rcu_segcblist_accelerate(&rdp->cblist, c);
- return;
- }
- raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
- needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
- raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
- if (needwake)
- rcu_gp_kthread_wake(rsp);
- }
- /*
- * Move any callbacks whose grace period has completed to the
- * RCU_DONE_TAIL sublist, then compact the remaining sublists and
- * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
- * sublist. This function is idempotent, so it does not hurt to
- * invoke it repeatedly. As long as it is not invoked -too- often...
- * Returns true if the RCU grace-period kthread needs to be awakened.
- *
- * The caller must hold rnp->lock with interrupts disabled.
- */
- static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
- struct rcu_data *rdp)
- {
- raw_lockdep_assert_held_rcu_node(rnp);
- /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
- if (!rcu_segcblist_pend_cbs(&rdp->cblist))
- return false;
- /*
- * Find all callbacks whose ->gp_seq numbers indicate that they
- * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
- */
- rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
- /* Classify any remaining callbacks. */
- return rcu_accelerate_cbs(rsp, rnp, rdp);
- }
- /*
- * Update CPU-local rcu_data state to record the beginnings and ends of
- * grace periods. The caller must hold the ->lock of the leaf rcu_node
- * structure corresponding to the current CPU, and must have irqs disabled.
- * Returns true if the grace-period kthread needs to be awakened.
- */
- static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
- struct rcu_data *rdp)
- {
- bool ret;
- bool need_gp;
- raw_lockdep_assert_held_rcu_node(rnp);
- if (rdp->gp_seq == rnp->gp_seq)
- return false; /* Nothing to do. */
- /* Handle the ends of any preceding grace periods first. */
- if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
- unlikely(READ_ONCE(rdp->gpwrap))) {
- ret = rcu_advance_cbs(rsp, rnp, rdp); /* Advance callbacks. */
- trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("cpuend"));
- } else {
- ret = rcu_accelerate_cbs(rsp, rnp, rdp); /* Recent callbacks. */
- }
- /* Now handle the beginnings of any new-to-this-CPU grace periods. */
- if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
- unlikely(READ_ONCE(rdp->gpwrap))) {
- /*
- * If the current grace period is waiting for this CPU,
- * set up to detect a quiescent state, otherwise don't
- * go looking for one.
- */
- trace_rcu_grace_period(rsp->name, rnp->gp_seq, TPS("cpustart"));
- need_gp = !!(rnp->qsmask & rdp->grpmask);
- rdp->cpu_no_qs.b.norm = need_gp;
- rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
- rdp->core_needs_qs = need_gp;
- zero_cpu_stall_ticks(rdp);
- }
- rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
- if (ULONG_CMP_GE(rnp->gp_seq_needed, rdp->gp_seq_needed) || rdp->gpwrap)
- rdp->gp_seq_needed = rnp->gp_seq_needed;
- WRITE_ONCE(rdp->gpwrap, false);
- rcu_gpnum_ovf(rnp, rdp);
- return ret;
- }
- static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
- {
- unsigned long flags;
- bool needwake;
- struct rcu_node *rnp;
- local_irq_save(flags);
- rnp = rdp->mynode;
- if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
- !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
- !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
- local_irq_restore(flags);
- return;
- }
- needwake = __note_gp_changes(rsp, rnp, rdp);
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- if (needwake)
- rcu_gp_kthread_wake(rsp);
- }
- static void rcu_gp_slow(struct rcu_state *rsp, int delay)
- {
- if (delay > 0 &&
- !(rcu_seq_ctr(rsp->gp_seq) %
- (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
- schedule_timeout_uninterruptible(delay);
- }
- /*
- * Initialize a new grace period. Return false if no grace period required.
- */
- static bool rcu_gp_init(struct rcu_state *rsp)
- {
- unsigned long flags;
- unsigned long oldmask;
- unsigned long mask;
- struct rcu_data *rdp;
- struct rcu_node *rnp = rcu_get_root(rsp);
- WRITE_ONCE(rsp->gp_activity, jiffies);
- raw_spin_lock_irq_rcu_node(rnp);
- if (!READ_ONCE(rsp->gp_flags)) {
- /* Spurious wakeup, tell caller to go back to sleep. */
- raw_spin_unlock_irq_rcu_node(rnp);
- return false;
- }
- WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */
- if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
- /*
- * Grace period already in progress, don't start another.
- * Not supposed to be able to happen.
- */
- raw_spin_unlock_irq_rcu_node(rnp);
- return false;
- }
- /* Advance to a new grace period and initialize state. */
- record_gp_stall_check_time(rsp);
- /* Record GP times before starting GP, hence rcu_seq_start(). */
- rcu_seq_start(&rsp->gp_seq);
- trace_rcu_grace_period(rsp->name, rsp->gp_seq, TPS("start"));
- raw_spin_unlock_irq_rcu_node(rnp);
- /*
- * Apply per-leaf buffered online and offline operations to the
- * rcu_node tree. Note that this new grace period need not wait
- * for subsequent online CPUs, and that quiescent-state forcing
- * will handle subsequent offline CPUs.
- */
- rsp->gp_state = RCU_GP_ONOFF;
- rcu_for_each_leaf_node(rsp, rnp) {
- spin_lock(&rsp->ofl_lock);
- raw_spin_lock_irq_rcu_node(rnp);
- if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
- !rnp->wait_blkd_tasks) {
- /* Nothing to do on this leaf rcu_node structure. */
- raw_spin_unlock_irq_rcu_node(rnp);
- spin_unlock(&rsp->ofl_lock);
- continue;
- }
- /* Record old state, apply changes to ->qsmaskinit field. */
- oldmask = rnp->qsmaskinit;
- rnp->qsmaskinit = rnp->qsmaskinitnext;
- /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
- if (!oldmask != !rnp->qsmaskinit) {
- if (!oldmask) { /* First online CPU for rcu_node. */
- if (!rnp->wait_blkd_tasks) /* Ever offline? */
- rcu_init_new_rnp(rnp);
- } else if (rcu_preempt_has_tasks(rnp)) {
- rnp->wait_blkd_tasks = true; /* blocked tasks */
- } else { /* Last offline CPU and can propagate. */
- rcu_cleanup_dead_rnp(rnp);
- }
- }
- /*
- * If all waited-on tasks from prior grace period are
- * done, and if all this rcu_node structure's CPUs are
- * still offline, propagate up the rcu_node tree and
- * clear ->wait_blkd_tasks. Otherwise, if one of this
- * rcu_node structure's CPUs has since come back online,
- * simply clear ->wait_blkd_tasks.
- */
- if (rnp->wait_blkd_tasks &&
- (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
- rnp->wait_blkd_tasks = false;
- if (!rnp->qsmaskinit)
- rcu_cleanup_dead_rnp(rnp);
- }
- raw_spin_unlock_irq_rcu_node(rnp);
- spin_unlock(&rsp->ofl_lock);
- }
- rcu_gp_slow(rsp, gp_preinit_delay); /* Races with CPU hotplug. */
- /*
- * Set the quiescent-state-needed bits in all the rcu_node
- * structures for all currently online CPUs in breadth-first order,
- * starting from the root rcu_node structure, relying on the layout
- * of the tree within the rsp->node[] array. Note that other CPUs
- * will access only the leaves of the hierarchy, thus seeing that no
- * grace period is in progress, at least until the corresponding
- * leaf node has been initialized.
- *
- * The grace period cannot complete until the initialization
- * process finishes, because this kthread handles both.
- */
- rsp->gp_state = RCU_GP_INIT;
- rcu_for_each_node_breadth_first(rsp, rnp) {
- rcu_gp_slow(rsp, gp_init_delay);
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- rdp = this_cpu_ptr(rsp->rda);
- rcu_preempt_check_blocked_tasks(rsp, rnp);
- rnp->qsmask = rnp->qsmaskinit;
- WRITE_ONCE(rnp->gp_seq, rsp->gp_seq);
- if (rnp == rdp->mynode)
- (void)__note_gp_changes(rsp, rnp, rdp);
- rcu_preempt_boost_start_gp(rnp);
- trace_rcu_grace_period_init(rsp->name, rnp->gp_seq,
- rnp->level, rnp->grplo,
- rnp->grphi, rnp->qsmask);
- /* Quiescent states for tasks on any now-offline CPUs. */
- mask = rnp->qsmask & ~rnp->qsmaskinitnext;
- rnp->rcu_gp_init_mask = mask;
- if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
- rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
- else
- raw_spin_unlock_irq_rcu_node(rnp);
- cond_resched_tasks_rcu_qs();
- WRITE_ONCE(rsp->gp_activity, jiffies);
- }
- return true;
- }
- /*
- * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
- * time.
- */
- static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
- {
- struct rcu_node *rnp = rcu_get_root(rsp);
- /* Someone like call_rcu() requested a force-quiescent-state scan. */
- *gfp = READ_ONCE(rsp->gp_flags);
- if (*gfp & RCU_GP_FLAG_FQS)
- return true;
- /* The current grace period has completed. */
- if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
- return true;
- return false;
- }
- /*
- * Do one round of quiescent-state forcing.
- */
- static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
- {
- struct rcu_node *rnp = rcu_get_root(rsp);
- WRITE_ONCE(rsp->gp_activity, jiffies);
- rsp->n_force_qs++;
- if (first_time) {
- /* Collect dyntick-idle snapshots. */
- force_qs_rnp(rsp, dyntick_save_progress_counter);
- } else {
- /* Handle dyntick-idle and offline CPUs. */
- force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
- }
- /* Clear flag to prevent immediate re-entry. */
- if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
- raw_spin_lock_irq_rcu_node(rnp);
- WRITE_ONCE(rsp->gp_flags,
- READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
- raw_spin_unlock_irq_rcu_node(rnp);
- }
- }
- /*
- * Clean up after the old grace period.
- */
- static void rcu_gp_cleanup(struct rcu_state *rsp)
- {
- unsigned long gp_duration;
- bool needgp = false;
- unsigned long new_gp_seq;
- struct rcu_data *rdp;
- struct rcu_node *rnp = rcu_get_root(rsp);
- struct swait_queue_head *sq;
- WRITE_ONCE(rsp->gp_activity, jiffies);
- raw_spin_lock_irq_rcu_node(rnp);
- gp_duration = jiffies - rsp->gp_start;
- if (gp_duration > rsp->gp_max)
- rsp->gp_max = gp_duration;
- /*
- * We know the grace period is complete, but to everyone else
- * it appears to still be ongoing. But it is also the case
- * that to everyone else it looks like there is nothing that
- * they can do to advance the grace period. It is therefore
- * safe for us to drop the lock in order to mark the grace
- * period as completed in all of the rcu_node structures.
- */
- raw_spin_unlock_irq_rcu_node(rnp);
- /*
- * Propagate new ->gp_seq value to rcu_node structures so that
- * other CPUs don't have to wait until the start of the next grace
- * period to process their callbacks. This also avoids some nasty
- * RCU grace-period initialization races by forcing the end of
- * the current grace period to be completely recorded in all of
- * the rcu_node structures before the beginning of the next grace
- * period is recorded in any of the rcu_node structures.
- */
- new_gp_seq = rsp->gp_seq;
- rcu_seq_end(&new_gp_seq);
- rcu_for_each_node_breadth_first(rsp, rnp) {
- raw_spin_lock_irq_rcu_node(rnp);
- if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
- dump_blkd_tasks(rsp, rnp, 10);
- WARN_ON_ONCE(rnp->qsmask);
- WRITE_ONCE(rnp->gp_seq, new_gp_seq);
- rdp = this_cpu_ptr(rsp->rda);
- if (rnp == rdp->mynode)
- needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
- /* smp_mb() provided by prior unlock-lock pair. */
- needgp = rcu_future_gp_cleanup(rsp, rnp) || needgp;
- sq = rcu_nocb_gp_get(rnp);
- raw_spin_unlock_irq_rcu_node(rnp);
- rcu_nocb_gp_cleanup(sq);
- cond_resched_tasks_rcu_qs();
- WRITE_ONCE(rsp->gp_activity, jiffies);
- rcu_gp_slow(rsp, gp_cleanup_delay);
- }
- rnp = rcu_get_root(rsp);
- raw_spin_lock_irq_rcu_node(rnp); /* GP before rsp->gp_seq update. */
- /* Declare grace period done. */
- rcu_seq_end(&rsp->gp_seq);
- trace_rcu_grace_period(rsp->name, rsp->gp_seq, TPS("end"));
- rsp->gp_state = RCU_GP_IDLE;
- /* Check for GP requests since above loop. */
- rdp = this_cpu_ptr(rsp->rda);
- if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
- trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
- TPS("CleanupMore"));
- needgp = true;
- }
- /* Advance CBs to reduce false positives below. */
- if (!rcu_accelerate_cbs(rsp, rnp, rdp) && needgp) {
- WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
- rsp->gp_req_activity = jiffies;
- trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq),
- TPS("newreq"));
- } else {
- WRITE_ONCE(rsp->gp_flags, rsp->gp_flags & RCU_GP_FLAG_INIT);
- }
- raw_spin_unlock_irq_rcu_node(rnp);
- }
- /*
- * Body of kthread that handles grace periods.
- */
- static int __noreturn rcu_gp_kthread(void *arg)
- {
- bool first_gp_fqs;
- int gf;
- unsigned long j;
- int ret;
- struct rcu_state *rsp = arg;
- struct rcu_node *rnp = rcu_get_root(rsp);
- rcu_bind_gp_kthread();
- for (;;) {
- /* Handle grace-period start. */
- for (;;) {
- trace_rcu_grace_period(rsp->name,
- READ_ONCE(rsp->gp_seq),
- TPS("reqwait"));
- rsp->gp_state = RCU_GP_WAIT_GPS;
- swait_event_idle_exclusive(rsp->gp_wq, READ_ONCE(rsp->gp_flags) &
- RCU_GP_FLAG_INIT);
- rsp->gp_state = RCU_GP_DONE_GPS;
- /* Locking provides needed memory barrier. */
- if (rcu_gp_init(rsp))
- break;
- cond_resched_tasks_rcu_qs();
- WRITE_ONCE(rsp->gp_activity, jiffies);
- WARN_ON(signal_pending(current));
- trace_rcu_grace_period(rsp->name,
- READ_ONCE(rsp->gp_seq),
- TPS("reqwaitsig"));
- }
- /* Handle quiescent-state forcing. */
- first_gp_fqs = true;
- j = jiffies_till_first_fqs;
- ret = 0;
- for (;;) {
- if (!ret) {
- rsp->jiffies_force_qs = jiffies + j;
- WRITE_ONCE(rsp->jiffies_kick_kthreads,
- jiffies + 3 * j);
- }
- trace_rcu_grace_period(rsp->name,
- READ_ONCE(rsp->gp_seq),
- TPS("fqswait"));
- rsp->gp_state = RCU_GP_WAIT_FQS;
- ret = swait_event_idle_timeout_exclusive(rsp->gp_wq,
- rcu_gp_fqs_check_wake(rsp, &gf), j);
- rsp->gp_state = RCU_GP_DOING_FQS;
- /* Locking provides needed memory barriers. */
- /* If grace period done, leave loop. */
- if (!READ_ONCE(rnp->qsmask) &&
- !rcu_preempt_blocked_readers_cgp(rnp))
- break;
- /* If time for quiescent-state forcing, do it. */
- if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
- (gf & RCU_GP_FLAG_FQS)) {
- trace_rcu_grace_period(rsp->name,
- READ_ONCE(rsp->gp_seq),
- TPS("fqsstart"));
- rcu_gp_fqs(rsp, first_gp_fqs);
- first_gp_fqs = false;
- trace_rcu_grace_period(rsp->name,
- READ_ONCE(rsp->gp_seq),
- TPS("fqsend"));
- cond_resched_tasks_rcu_qs();
- WRITE_ONCE(rsp->gp_activity, jiffies);
- ret = 0; /* Force full wait till next FQS. */
- j = jiffies_till_next_fqs;
- } else {
- /* Deal with stray signal. */
- cond_resched_tasks_rcu_qs();
- WRITE_ONCE(rsp->gp_activity, jiffies);
- WARN_ON(signal_pending(current));
- trace_rcu_grace_period(rsp->name,
- READ_ONCE(rsp->gp_seq),
- TPS("fqswaitsig"));
- ret = 1; /* Keep old FQS timing. */
- j = jiffies;
- if (time_after(jiffies, rsp->jiffies_force_qs))
- j = 1;
- else
- j = rsp->jiffies_force_qs - j;
- }
- }
- /* Handle grace-period end. */
- rsp->gp_state = RCU_GP_CLEANUP;
- rcu_gp_cleanup(rsp);
- rsp->gp_state = RCU_GP_CLEANED;
- }
- }
- /*
- * Report a full set of quiescent states to the specified rcu_state data
- * structure. Invoke rcu_gp_kthread_wake() to awaken the grace-period
- * kthread if another grace period is required. Whether we wake
- * the grace-period kthread or it awakens itself for the next round
- * of quiescent-state forcing, that kthread will clean up after the
- * just-completed grace period. Note that the caller must hold rnp->lock,
- * which is released before return.
- */
- static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
- __releases(rcu_get_root(rsp)->lock)
- {
- raw_lockdep_assert_held_rcu_node(rcu_get_root(rsp));
- WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
- WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
- raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
- rcu_gp_kthread_wake(rsp);
- }
- /*
- * Similar to rcu_report_qs_rdp(), for which it is a helper function.
- * Allows quiescent states for a group of CPUs to be reported at one go
- * to the specified rcu_node structure, though all the CPUs in the group
- * must be represented by the same rcu_node structure (which need not be a
- * leaf rcu_node structure, though it often will be). The gps parameter
- * is the grace-period snapshot, which means that the quiescent states
- * are valid only if rnp->gp_seq is equal to gps. That structure's lock
- * must be held upon entry, and it is released before return.
- *
- * As a special case, if mask is zero, the bit-already-cleared check is
- * disabled. This allows propagating quiescent state due to resumed tasks
- * during grace-period initialization.
- */
- static void
- rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
- struct rcu_node *rnp, unsigned long gps, unsigned long flags)
- __releases(rnp->lock)
- {
- unsigned long oldmask = 0;
- struct rcu_node *rnp_c;
- raw_lockdep_assert_held_rcu_node(rnp);
- /* Walk up the rcu_node hierarchy. */
- for (;;) {
- if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
- /*
- * Our bit has already been cleared, or the
- * relevant grace period is already over, so done.
- */
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return;
- }
- WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
- WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
- rcu_preempt_blocked_readers_cgp(rnp));
- rnp->qsmask &= ~mask;
- trace_rcu_quiescent_state_report(rsp->name, rnp->gp_seq,
- mask, rnp->qsmask, rnp->level,
- rnp->grplo, rnp->grphi,
- !!rnp->gp_tasks);
- if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
- /* Other bits still set at this level, so done. */
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return;
- }
- rnp->completedqs = rnp->gp_seq;
- mask = rnp->grpmask;
- if (rnp->parent == NULL) {
- /* No more levels. Exit loop holding root lock. */
- break;
- }
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- rnp_c = rnp;
- rnp = rnp->parent;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- oldmask = rnp_c->qsmask;
- }
- /*
- * Get here if we are the last CPU to pass through a quiescent
- * state for this grace period. Invoke rcu_report_qs_rsp()
- * to clean up and start the next grace period if one is needed.
- */
- rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
- }
- /*
- * Record a quiescent state for all tasks that were previously queued
- * on the specified rcu_node structure and that were blocking the current
- * RCU grace period. The caller must hold the specified rnp->lock with
- * irqs disabled, and this lock is released upon return, but irqs remain
- * disabled.
- */
- static void __maybe_unused
- rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
- struct rcu_node *rnp, unsigned long flags)
- __releases(rnp->lock)
- {
- unsigned long gps;
- unsigned long mask;
- struct rcu_node *rnp_p;
- raw_lockdep_assert_held_rcu_node(rnp);
- if (WARN_ON_ONCE(rcu_state_p == &rcu_sched_state) ||
- WARN_ON_ONCE(rsp != rcu_state_p) ||
- WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
- rnp->qsmask != 0) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return; /* Still need more quiescent states! */
- }
- rnp->completedqs = rnp->gp_seq;
- rnp_p = rnp->parent;
- if (rnp_p == NULL) {
- /*
- * Only one rcu_node structure in the tree, so don't
- * try to report up to its nonexistent parent!
- */
- rcu_report_qs_rsp(rsp, flags);
- return;
- }
- /* Report up the rest of the hierarchy, tracking current ->gp_seq. */
- gps = rnp->gp_seq;
- mask = rnp->grpmask;
- raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
- raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
- rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
- }
- /*
- * Record a quiescent state for the specified CPU to that CPU's rcu_data
- * structure. This must be called from the specified CPU.
- */
- static void
- rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
- {
- unsigned long flags;
- unsigned long mask;
- bool needwake;
- struct rcu_node *rnp;
- rnp = rdp->mynode;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
- rdp->gpwrap) {
- /*
- * The grace period in which this quiescent state was
- * recorded has ended, so don't report it upwards.
- * We will instead need a new quiescent state that lies
- * within the current grace period.
- */
- rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
- rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return;
- }
- mask = rdp->grpmask;
- if ((rnp->qsmask & mask) == 0) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- } else {
- rdp->core_needs_qs = false;
- /*
- * This GP can't end until cpu checks in, so all of our
- * callbacks can be processed during the next GP.
- */
- needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
- rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
- /* ^^^ Released rnp->lock */
- if (needwake)
- rcu_gp_kthread_wake(rsp);
- }
- }
- /*
- * Check to see if there is a new grace period of which this CPU
- * is not yet aware, and if so, set up local rcu_data state for it.
- * Otherwise, see if this CPU has just passed through its first
- * quiescent state for this grace period, and record that fact if so.
- */
- static void
- rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
- {
- /* Check for grace-period ends and beginnings. */
- note_gp_changes(rsp, rdp);
- /*
- * Does this CPU still need to do its part for current grace period?
- * If no, return and let the other CPUs do their part as well.
- */
- if (!rdp->core_needs_qs)
- return;
- /*
- * Was there a quiescent state since the beginning of the grace
- * period? If no, then exit and wait for the next call.
- */
- if (rdp->cpu_no_qs.b.norm)
- return;
- /*
- * Tell RCU we are done (but rcu_report_qs_rdp() will be the
- * judge of that).
- */
- rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
- }
- /*
- * Trace the fact that this CPU is going offline.
- */
- static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
- {
- RCU_TRACE(bool blkd;)
- RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda);)
- RCU_TRACE(struct rcu_node *rnp = rdp->mynode;)
- if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
- return;
- RCU_TRACE(blkd = !!(rnp->qsmask & rdp->grpmask);)
- trace_rcu_grace_period(rsp->name, rnp->gp_seq,
- blkd ? TPS("cpuofl") : TPS("cpuofl-bgp"));
- }
- /*
- * All CPUs for the specified rcu_node structure have gone offline,
- * and all tasks that were preempted within an RCU read-side critical
- * section while running on one of those CPUs have since exited their RCU
- * read-side critical section. Some other CPU is reporting this fact with
- * the specified rcu_node structure's ->lock held and interrupts disabled.
- * This function therefore goes up the tree of rcu_node structures,
- * clearing the corresponding bits in the ->qsmaskinit fields. Note that
- * the leaf rcu_node structure's ->qsmaskinit field has already been
- * updated.
- *
- * This function does check that the specified rcu_node structure has
- * all CPUs offline and no blocked tasks, so it is OK to invoke it
- * prematurely. That said, invoking it after the fact will cost you
- * a needless lock acquisition. So once it has done its work, don't
- * invoke it again.
- */
- static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
- {
- long mask;
- struct rcu_node *rnp = rnp_leaf;
- raw_lockdep_assert_held_rcu_node(rnp_leaf);
- if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
- WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
- WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
- return;
- for (;;) {
- mask = rnp->grpmask;
- rnp = rnp->parent;
- if (!rnp)
- break;
- raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
- rnp->qsmaskinit &= ~mask;
- /* Between grace periods, so better already be zero! */
- WARN_ON_ONCE(rnp->qsmask);
- if (rnp->qsmaskinit) {
- raw_spin_unlock_rcu_node(rnp);
- /* irqs remain disabled. */
- return;
- }
- raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
- }
- }
- /*
- * The CPU has been completely removed, and some other CPU is reporting
- * this fact from process context. Do the remainder of the cleanup.
- * There can only be one CPU hotplug operation at a time, so no need for
- * explicit locking.
- */
- static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
- {
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
- if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
- return;
- /* Adjust any no-longer-needed kthreads. */
- rcu_boost_kthread_setaffinity(rnp, -1);
- }
- /*
- * Invoke any RCU callbacks that have made it to the end of their grace
- * period. Thottle as specified by rdp->blimit.
- */
- static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
- {
- unsigned long flags;
- struct rcu_head *rhp;
- struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
- long bl, count;
- /* If no callbacks are ready, just return. */
- if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
- trace_rcu_batch_start(rsp->name,
- rcu_segcblist_n_lazy_cbs(&rdp->cblist),
- rcu_segcblist_n_cbs(&rdp->cblist), 0);
- trace_rcu_batch_end(rsp->name, 0,
- !rcu_segcblist_empty(&rdp->cblist),
- need_resched(), is_idle_task(current),
- rcu_is_callbacks_kthread());
- return;
- }
- /*
- * Extract the list of ready callbacks, disabling to prevent
- * races with call_rcu() from interrupt handlers. Leave the
- * callback counts, as rcu_barrier() needs to be conservative.
- */
- local_irq_save(flags);
- WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
- bl = rdp->blimit;
- trace_rcu_batch_start(rsp->name, rcu_segcblist_n_lazy_cbs(&rdp->cblist),
- rcu_segcblist_n_cbs(&rdp->cblist), bl);
- rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
- local_irq_restore(flags);
- /* Invoke callbacks. */
- rhp = rcu_cblist_dequeue(&rcl);
- for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
- debug_rcu_head_unqueue(rhp);
- if (__rcu_reclaim(rsp->name, rhp))
- rcu_cblist_dequeued_lazy(&rcl);
- /*
- * Stop only if limit reached and CPU has something to do.
- * Note: The rcl structure counts down from zero.
- */
- if (-rcl.len >= bl &&
- (need_resched() ||
- (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
- break;
- }
- local_irq_save(flags);
- count = -rcl.len;
- trace_rcu_batch_end(rsp->name, count, !!rcl.head, need_resched(),
- is_idle_task(current), rcu_is_callbacks_kthread());
- /* Update counts and requeue any remaining callbacks. */
- rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
- smp_mb(); /* List handling before counting for rcu_barrier(). */
- rcu_segcblist_insert_count(&rdp->cblist, &rcl);
- /* Reinstate batch limit if we have worked down the excess. */
- count = rcu_segcblist_n_cbs(&rdp->cblist);
- if (rdp->blimit == LONG_MAX && count <= qlowmark)
- rdp->blimit = blimit;
- /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
- if (count == 0 && rdp->qlen_last_fqs_check != 0) {
- rdp->qlen_last_fqs_check = 0;
- rdp->n_force_qs_snap = rsp->n_force_qs;
- } else if (count < rdp->qlen_last_fqs_check - qhimark)
- rdp->qlen_last_fqs_check = count;
- /*
- * The following usually indicates a double call_rcu(). To track
- * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
- */
- WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
- local_irq_restore(flags);
- /* Re-invoke RCU core processing if there are callbacks remaining. */
- if (rcu_segcblist_ready_cbs(&rdp->cblist))
- invoke_rcu_core();
- }
- /*
- * Check to see if this CPU is in a non-context-switch quiescent state
- * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
- * Also schedule RCU core processing.
- *
- * This function must be called from hardirq context. It is normally
- * invoked from the scheduling-clock interrupt.
- */
- void rcu_check_callbacks(int user)
- {
- trace_rcu_utilization(TPS("Start scheduler-tick"));
- increment_cpu_stall_ticks();
- if (user || rcu_is_cpu_rrupt_from_idle()) {
- /*
- * Get here if this CPU took its interrupt from user
- * mode or from the idle loop, and if this is not a
- * nested interrupt. In this case, the CPU is in
- * a quiescent state, so note it.
- *
- * No memory barrier is required here because both
- * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
- * variables that other CPUs neither access nor modify,
- * at least not while the corresponding CPU is online.
- */
- rcu_sched_qs();
- rcu_bh_qs();
- rcu_note_voluntary_context_switch(current);
- } else if (!in_softirq()) {
- /*
- * Get here if this CPU did not take its interrupt from
- * softirq, in other words, if it is not interrupting
- * a rcu_bh read-side critical section. This is an _bh
- * critical section, so note it.
- */
- rcu_bh_qs();
- }
- rcu_preempt_check_callbacks();
- /* The load-acquire pairs with the store-release setting to true. */
- if (smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
- /* Idle and userspace execution already are quiescent states. */
- if (!rcu_is_cpu_rrupt_from_idle() && !user) {
- set_tsk_need_resched(current);
- set_preempt_need_resched();
- }
- __this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
- }
- if (rcu_pending())
- invoke_rcu_core();
- trace_rcu_utilization(TPS("End scheduler-tick"));
- }
- /*
- * Scan the leaf rcu_node structures, processing dyntick state for any that
- * have not yet encountered a quiescent state, using the function specified.
- * Also initiate boosting for any threads blocked on the root rcu_node.
- *
- * The caller must have suppressed start of new grace periods.
- */
- static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp))
- {
- int cpu;
- unsigned long flags;
- unsigned long mask;
- struct rcu_node *rnp;
- rcu_for_each_leaf_node(rsp, rnp) {
- cond_resched_tasks_rcu_qs();
- mask = 0;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- if (rnp->qsmask == 0) {
- if (rcu_state_p == &rcu_sched_state ||
- rsp != rcu_state_p ||
- rcu_preempt_blocked_readers_cgp(rnp)) {
- /*
- * No point in scanning bits because they
- * are all zero. But we might need to
- * priority-boost blocked readers.
- */
- rcu_initiate_boost(rnp, flags);
- /* rcu_initiate_boost() releases rnp->lock */
- continue;
- }
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- continue;
- }
- for_each_leaf_node_possible_cpu(rnp, cpu) {
- unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
- if ((rnp->qsmask & bit) != 0) {
- if (f(per_cpu_ptr(rsp->rda, cpu)))
- mask |= bit;
- }
- }
- if (mask != 0) {
- /* Idle/offline CPUs, report (releases rnp->lock). */
- rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
- } else {
- /* Nothing to do here, so just drop the lock. */
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- }
- }
- /*
- * Force quiescent states on reluctant CPUs, and also detect which
- * CPUs are in dyntick-idle mode.
- */
- static void force_quiescent_state(struct rcu_state *rsp)
- {
- unsigned long flags;
- bool ret;
- struct rcu_node *rnp;
- struct rcu_node *rnp_old = NULL;
- /* Funnel through hierarchy to reduce memory contention. */
- rnp = __this_cpu_read(rsp->rda->mynode);
- for (; rnp != NULL; rnp = rnp->parent) {
- ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
- !raw_spin_trylock(&rnp->fqslock);
- if (rnp_old != NULL)
- raw_spin_unlock(&rnp_old->fqslock);
- if (ret)
- return;
- rnp_old = rnp;
- }
- /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
- /* Reached the root of the rcu_node tree, acquire lock. */
- raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
- raw_spin_unlock(&rnp_old->fqslock);
- if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
- raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
- return; /* Someone beat us to it. */
- }
- WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
- raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
- rcu_gp_kthread_wake(rsp);
- }
- /*
- * This function checks for grace-period requests that fail to motivate
- * RCU to come out of its idle mode.
- */
- static void
- rcu_check_gp_start_stall(struct rcu_state *rsp, struct rcu_node *rnp,
- struct rcu_data *rdp)
- {
- const unsigned long gpssdelay = rcu_jiffies_till_stall_check() * HZ;
- unsigned long flags;
- unsigned long j;
- struct rcu_node *rnp_root = rcu_get_root(rsp);
- static atomic_t warned = ATOMIC_INIT(0);
- if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress(rsp) ||
- ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
- return;
- j = jiffies; /* Expensive access, and in common case don't get here. */
- if (time_before(j, READ_ONCE(rsp->gp_req_activity) + gpssdelay) ||
- time_before(j, READ_ONCE(rsp->gp_activity) + gpssdelay) ||
- atomic_read(&warned))
- return;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- j = jiffies;
- if (rcu_gp_in_progress(rsp) ||
- ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
- time_before(j, READ_ONCE(rsp->gp_req_activity) + gpssdelay) ||
- time_before(j, READ_ONCE(rsp->gp_activity) + gpssdelay) ||
- atomic_read(&warned)) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return;
- }
- /* Hold onto the leaf lock to make others see warned==1. */
- if (rnp_root != rnp)
- raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
- j = jiffies;
- if (rcu_gp_in_progress(rsp) ||
- ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
- time_before(j, rsp->gp_req_activity + gpssdelay) ||
- time_before(j, rsp->gp_activity + gpssdelay) ||
- atomic_xchg(&warned, 1)) {
- raw_spin_unlock_rcu_node(rnp_root); /* irqs remain disabled. */
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return;
- }
- pr_alert("%s: g%ld->%ld gar:%lu ga:%lu f%#x gs:%d %s->state:%#lx\n",
- __func__, (long)READ_ONCE(rsp->gp_seq),
- (long)READ_ONCE(rnp_root->gp_seq_needed),
- j - rsp->gp_req_activity, j - rsp->gp_activity,
- rsp->gp_flags, rsp->gp_state, rsp->name,
- rsp->gp_kthread ? rsp->gp_kthread->state : 0x1ffffL);
- WARN_ON(1);
- if (rnp_root != rnp)
- raw_spin_unlock_rcu_node(rnp_root);
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- /*
- * This does the RCU core processing work for the specified rcu_state
- * and rcu_data structures. This may be called only from the CPU to
- * whom the rdp belongs.
- */
- static void
- __rcu_process_callbacks(struct rcu_state *rsp)
- {
- unsigned long flags;
- struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
- struct rcu_node *rnp = rdp->mynode;
- WARN_ON_ONCE(!rdp->beenonline);
- /* Update RCU state based on any recent quiescent states. */
- rcu_check_quiescent_state(rsp, rdp);
- /* No grace period and unregistered callbacks? */
- if (!rcu_gp_in_progress(rsp) &&
- rcu_segcblist_is_enabled(&rdp->cblist)) {
- local_irq_save(flags);
- if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
- rcu_accelerate_cbs_unlocked(rsp, rnp, rdp);
- local_irq_restore(flags);
- }
- rcu_check_gp_start_stall(rsp, rnp, rdp);
- /* If there are callbacks ready, invoke them. */
- if (rcu_segcblist_ready_cbs(&rdp->cblist))
- invoke_rcu_callbacks(rsp, rdp);
- /* Do any needed deferred wakeups of rcuo kthreads. */
- do_nocb_deferred_wakeup(rdp);
- }
- /*
- * Do RCU core processing for the current CPU.
- */
- static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
- {
- struct rcu_state *rsp;
- if (cpu_is_offline(smp_processor_id()))
- return;
- trace_rcu_utilization(TPS("Start RCU core"));
- for_each_rcu_flavor(rsp)
- __rcu_process_callbacks(rsp);
- trace_rcu_utilization(TPS("End RCU core"));
- }
- /*
- * Schedule RCU callback invocation. If the specified type of RCU
- * does not support RCU priority boosting, just do a direct call,
- * otherwise wake up the per-CPU kernel kthread. Note that because we
- * are running on the current CPU with softirqs disabled, the
- * rcu_cpu_kthread_task cannot disappear out from under us.
- */
- static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
- {
- if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
- return;
- if (likely(!rsp->boost)) {
- rcu_do_batch(rsp, rdp);
- return;
- }
- invoke_rcu_callbacks_kthread();
- }
- static void invoke_rcu_core(void)
- {
- if (cpu_online(smp_processor_id()))
- raise_softirq(RCU_SOFTIRQ);
- }
- /*
- * Handle any core-RCU processing required by a call_rcu() invocation.
- */
- static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
- struct rcu_head *head, unsigned long flags)
- {
- /*
- * If called from an extended quiescent state, invoke the RCU
- * core in order to force a re-evaluation of RCU's idleness.
- */
- if (!rcu_is_watching())
- invoke_rcu_core();
- /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
- if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
- return;
- /*
- * Force the grace period if too many callbacks or too long waiting.
- * Enforce hysteresis, and don't invoke force_quiescent_state()
- * if some other CPU has recently done so. Also, don't bother
- * invoking force_quiescent_state() if the newly enqueued callback
- * is the only one waiting for a grace period to complete.
- */
- if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
- rdp->qlen_last_fqs_check + qhimark)) {
- /* Are we ignoring a completed grace period? */
- note_gp_changes(rsp, rdp);
- /* Start a new grace period if one not already started. */
- if (!rcu_gp_in_progress(rsp)) {
- rcu_accelerate_cbs_unlocked(rsp, rdp->mynode, rdp);
- } else {
- /* Give the grace period a kick. */
- rdp->blimit = LONG_MAX;
- if (rsp->n_force_qs == rdp->n_force_qs_snap &&
- rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
- force_quiescent_state(rsp);
- rdp->n_force_qs_snap = rsp->n_force_qs;
- rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
- }
- }
- }
- /*
- * RCU callback function to leak a callback.
- */
- static void rcu_leak_callback(struct rcu_head *rhp)
- {
- }
- /*
- * Helper function for call_rcu() and friends. The cpu argument will
- * normally be -1, indicating "currently running CPU". It may specify
- * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
- * is expected to specify a CPU.
- */
- static void
- __call_rcu(struct rcu_head *head, rcu_callback_t func,
- struct rcu_state *rsp, int cpu, bool lazy)
- {
- unsigned long flags;
- struct rcu_data *rdp;
- /* Misaligned rcu_head! */
- WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
- if (debug_rcu_head_queue(head)) {
- /*
- * Probable double call_rcu(), so leak the callback.
- * Use rcu:rcu_callback trace event to find the previous
- * time callback was passed to __call_rcu().
- */
- WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pF()!!!\n",
- head, head->func);
- WRITE_ONCE(head->func, rcu_leak_callback);
- return;
- }
- head->func = func;
- head->next = NULL;
- local_irq_save(flags);
- rdp = this_cpu_ptr(rsp->rda);
- /* Add the callback to our list. */
- if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist)) || cpu != -1) {
- int offline;
- if (cpu != -1)
- rdp = per_cpu_ptr(rsp->rda, cpu);
- if (likely(rdp->mynode)) {
- /* Post-boot, so this should be for a no-CBs CPU. */
- offline = !__call_rcu_nocb(rdp, head, lazy, flags);
- WARN_ON_ONCE(offline);
- /* Offline CPU, _call_rcu() illegal, leak callback. */
- local_irq_restore(flags);
- return;
- }
- /*
- * Very early boot, before rcu_init(). Initialize if needed
- * and then drop through to queue the callback.
- */
- BUG_ON(cpu != -1);
- WARN_ON_ONCE(!rcu_is_watching());
- if (rcu_segcblist_empty(&rdp->cblist))
- rcu_segcblist_init(&rdp->cblist);
- }
- rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
- if (!lazy)
- rcu_idle_count_callbacks_posted();
- if (__is_kfree_rcu_offset((unsigned long)func))
- trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
- rcu_segcblist_n_lazy_cbs(&rdp->cblist),
- rcu_segcblist_n_cbs(&rdp->cblist));
- else
- trace_rcu_callback(rsp->name, head,
- rcu_segcblist_n_lazy_cbs(&rdp->cblist),
- rcu_segcblist_n_cbs(&rdp->cblist));
- /* Go handle any RCU core processing required. */
- __call_rcu_core(rsp, rdp, head, flags);
- local_irq_restore(flags);
- }
- /**
- * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
- * @head: structure to be used for queueing the RCU updates.
- * @func: actual callback function to be invoked after the grace period
- *
- * The callback function will be invoked some time after a full grace
- * period elapses, in other words after all currently executing RCU
- * read-side critical sections have completed. call_rcu_sched() assumes
- * that the read-side critical sections end on enabling of preemption
- * or on voluntary preemption.
- * RCU read-side critical sections are delimited by:
- *
- * - rcu_read_lock_sched() and rcu_read_unlock_sched(), OR
- * - anything that disables preemption.
- *
- * These may be nested.
- *
- * See the description of call_rcu() for more detailed information on
- * memory ordering guarantees.
- */
- void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
- {
- __call_rcu(head, func, &rcu_sched_state, -1, 0);
- }
- EXPORT_SYMBOL_GPL(call_rcu_sched);
- /**
- * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
- * @head: structure to be used for queueing the RCU updates.
- * @func: actual callback function to be invoked after the grace period
- *
- * The callback function will be invoked some time after a full grace
- * period elapses, in other words after all currently executing RCU
- * read-side critical sections have completed. call_rcu_bh() assumes
- * that the read-side critical sections end on completion of a softirq
- * handler. This means that read-side critical sections in process
- * context must not be interrupted by softirqs. This interface is to be
- * used when most of the read-side critical sections are in softirq context.
- * RCU read-side critical sections are delimited by:
- *
- * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context, OR
- * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
- *
- * These may be nested.
- *
- * See the description of call_rcu() for more detailed information on
- * memory ordering guarantees.
- */
- void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
- {
- __call_rcu(head, func, &rcu_bh_state, -1, 0);
- }
- EXPORT_SYMBOL_GPL(call_rcu_bh);
- /*
- * Queue an RCU callback for lazy invocation after a grace period.
- * This will likely be later named something like "call_rcu_lazy()",
- * but this change will require some way of tagging the lazy RCU
- * callbacks in the list of pending callbacks. Until then, this
- * function may only be called from __kfree_rcu().
- */
- void kfree_call_rcu(struct rcu_head *head,
- rcu_callback_t func)
- {
- __call_rcu(head, func, rcu_state_p, -1, 1);
- }
- EXPORT_SYMBOL_GPL(kfree_call_rcu);
- /*
- * Because a context switch is a grace period for RCU-sched and RCU-bh,
- * any blocking grace-period wait automatically implies a grace period
- * if there is only one CPU online at any point time during execution
- * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
- * occasionally incorrectly indicate that there are multiple CPUs online
- * when there was in fact only one the whole time, as this just adds
- * some overhead: RCU still operates correctly.
- */
- static int rcu_blocking_is_gp(void)
- {
- int ret;
- might_sleep(); /* Check for RCU read-side critical section. */
- preempt_disable();
- ret = num_online_cpus() <= 1;
- preempt_enable();
- return ret;
- }
- /**
- * synchronize_sched - wait until an rcu-sched grace period has elapsed.
- *
- * Control will return to the caller some time after a full rcu-sched
- * grace period has elapsed, in other words after all currently executing
- * rcu-sched read-side critical sections have completed. These read-side
- * critical sections are delimited by rcu_read_lock_sched() and
- * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
- * local_irq_disable(), and so on may be used in place of
- * rcu_read_lock_sched().
- *
- * This means that all preempt_disable code sequences, including NMI and
- * non-threaded hardware-interrupt handlers, in progress on entry will
- * have completed before this primitive returns. However, this does not
- * guarantee that softirq handlers will have completed, since in some
- * kernels, these handlers can run in process context, and can block.
- *
- * Note that this guarantee implies further memory-ordering guarantees.
- * On systems with more than one CPU, when synchronize_sched() returns,
- * each CPU is guaranteed to have executed a full memory barrier since the
- * end of its last RCU-sched read-side critical section whose beginning
- * preceded the call to synchronize_sched(). In addition, each CPU having
- * an RCU read-side critical section that extends beyond the return from
- * synchronize_sched() is guaranteed to have executed a full memory barrier
- * after the beginning of synchronize_sched() and before the beginning of
- * that RCU read-side critical section. Note that these guarantees include
- * CPUs that are offline, idle, or executing in user mode, as well as CPUs
- * that are executing in the kernel.
- *
- * Furthermore, if CPU A invoked synchronize_sched(), which returned
- * to its caller on CPU B, then both CPU A and CPU B are guaranteed
- * to have executed a full memory barrier during the execution of
- * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
- * again only if the system has more than one CPU).
- */
- void synchronize_sched(void)
- {
- RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
- lock_is_held(&rcu_lock_map) ||
- lock_is_held(&rcu_sched_lock_map),
- "Illegal synchronize_sched() in RCU-sched read-side critical section");
- if (rcu_blocking_is_gp())
- return;
- if (rcu_gp_is_expedited())
- synchronize_sched_expedited();
- else
- wait_rcu_gp(call_rcu_sched);
- }
- EXPORT_SYMBOL_GPL(synchronize_sched);
- /**
- * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
- *
- * Control will return to the caller some time after a full rcu_bh grace
- * period has elapsed, in other words after all currently executing rcu_bh
- * read-side critical sections have completed. RCU read-side critical
- * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
- * and may be nested.
- *
- * See the description of synchronize_sched() for more detailed information
- * on memory ordering guarantees.
- */
- void synchronize_rcu_bh(void)
- {
- RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
- lock_is_held(&rcu_lock_map) ||
- lock_is_held(&rcu_sched_lock_map),
- "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
- if (rcu_blocking_is_gp())
- return;
- if (rcu_gp_is_expedited())
- synchronize_rcu_bh_expedited();
- else
- wait_rcu_gp(call_rcu_bh);
- }
- EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
- /**
- * get_state_synchronize_rcu - Snapshot current RCU state
- *
- * Returns a cookie that is used by a later call to cond_synchronize_rcu()
- * to determine whether or not a full grace period has elapsed in the
- * meantime.
- */
- unsigned long get_state_synchronize_rcu(void)
- {
- /*
- * Any prior manipulation of RCU-protected data must happen
- * before the load from ->gp_seq.
- */
- smp_mb(); /* ^^^ */
- return rcu_seq_snap(&rcu_state_p->gp_seq);
- }
- EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
- /**
- * cond_synchronize_rcu - Conditionally wait for an RCU grace period
- *
- * @oldstate: return value from earlier call to get_state_synchronize_rcu()
- *
- * If a full RCU grace period has elapsed since the earlier call to
- * get_state_synchronize_rcu(), just return. Otherwise, invoke
- * synchronize_rcu() to wait for a full grace period.
- *
- * Yes, this function does not take counter wrap into account. But
- * counter wrap is harmless. If the counter wraps, we have waited for
- * more than 2 billion grace periods (and way more on a 64-bit system!),
- * so waiting for one additional grace period should be just fine.
- */
- void cond_synchronize_rcu(unsigned long oldstate)
- {
- if (!rcu_seq_done(&rcu_state_p->gp_seq, oldstate))
- synchronize_rcu();
- else
- smp_mb(); /* Ensure GP ends before subsequent accesses. */
- }
- EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
- /**
- * get_state_synchronize_sched - Snapshot current RCU-sched state
- *
- * Returns a cookie that is used by a later call to cond_synchronize_sched()
- * to determine whether or not a full grace period has elapsed in the
- * meantime.
- */
- unsigned long get_state_synchronize_sched(void)
- {
- /*
- * Any prior manipulation of RCU-protected data must happen
- * before the load from ->gp_seq.
- */
- smp_mb(); /* ^^^ */
- return rcu_seq_snap(&rcu_sched_state.gp_seq);
- }
- EXPORT_SYMBOL_GPL(get_state_synchronize_sched);
- /**
- * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
- *
- * @oldstate: return value from earlier call to get_state_synchronize_sched()
- *
- * If a full RCU-sched grace period has elapsed since the earlier call to
- * get_state_synchronize_sched(), just return. Otherwise, invoke
- * synchronize_sched() to wait for a full grace period.
- *
- * Yes, this function does not take counter wrap into account. But
- * counter wrap is harmless. If the counter wraps, we have waited for
- * more than 2 billion grace periods (and way more on a 64-bit system!),
- * so waiting for one additional grace period should be just fine.
- */
- void cond_synchronize_sched(unsigned long oldstate)
- {
- if (!rcu_seq_done(&rcu_sched_state.gp_seq, oldstate))
- synchronize_sched();
- else
- smp_mb(); /* Ensure GP ends before subsequent accesses. */
- }
- EXPORT_SYMBOL_GPL(cond_synchronize_sched);
- /*
- * Check to see if there is any immediate RCU-related work to be done
- * by the current CPU, for the specified type of RCU, returning 1 if so.
- * The checks are in order of increasing expense: checks that can be
- * carried out against CPU-local state are performed first. However,
- * we must check for CPU stalls first, else we might not get a chance.
- */
- static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
- {
- struct rcu_node *rnp = rdp->mynode;
- /* Check for CPU stalls, if enabled. */
- check_cpu_stall(rsp, rdp);
- /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
- if (rcu_nohz_full_cpu(rsp))
- return 0;
- /* Is the RCU core waiting for a quiescent state from this CPU? */
- if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm)
- return 1;
- /* Does this CPU have callbacks ready to invoke? */
- if (rcu_segcblist_ready_cbs(&rdp->cblist))
- return 1;
- /* Has RCU gone idle with this CPU needing another grace period? */
- if (!rcu_gp_in_progress(rsp) &&
- rcu_segcblist_is_enabled(&rdp->cblist) &&
- !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
- return 1;
- /* Have RCU grace period completed or started? */
- if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
- unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
- return 1;
- /* Does this CPU need a deferred NOCB wakeup? */
- if (rcu_nocb_need_deferred_wakeup(rdp))
- return 1;
- /* nothing to do */
- return 0;
- }
- /*
- * Check to see if there is any immediate RCU-related work to be done
- * by the current CPU, returning 1 if so. This function is part of the
- * RCU implementation; it is -not- an exported member of the RCU API.
- */
- static int rcu_pending(void)
- {
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp)
- if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
- return 1;
- return 0;
- }
- /*
- * Return true if the specified CPU has any callback. If all_lazy is
- * non-NULL, store an indication of whether all callbacks are lazy.
- * (If there are no callbacks, all of them are deemed to be lazy.)
- */
- static bool rcu_cpu_has_callbacks(bool *all_lazy)
- {
- bool al = true;
- bool hc = false;
- struct rcu_data *rdp;
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp) {
- rdp = this_cpu_ptr(rsp->rda);
- if (rcu_segcblist_empty(&rdp->cblist))
- continue;
- hc = true;
- if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist) || !all_lazy) {
- al = false;
- break;
- }
- }
- if (all_lazy)
- *all_lazy = al;
- return hc;
- }
- /*
- * Helper function for _rcu_barrier() tracing. If tracing is disabled,
- * the compiler is expected to optimize this away.
- */
- static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
- int cpu, unsigned long done)
- {
- trace_rcu_barrier(rsp->name, s, cpu,
- atomic_read(&rsp->barrier_cpu_count), done);
- }
- /*
- * RCU callback function for _rcu_barrier(). If we are last, wake
- * up the task executing _rcu_barrier().
- */
- static void rcu_barrier_callback(struct rcu_head *rhp)
- {
- struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
- struct rcu_state *rsp = rdp->rsp;
- if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
- _rcu_barrier_trace(rsp, TPS("LastCB"), -1,
- rsp->barrier_sequence);
- complete(&rsp->barrier_completion);
- } else {
- _rcu_barrier_trace(rsp, TPS("CB"), -1, rsp->barrier_sequence);
- }
- }
- /*
- * Called with preemption disabled, and from cross-cpu IRQ context.
- */
- static void rcu_barrier_func(void *type)
- {
- struct rcu_state *rsp = type;
- struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
- _rcu_barrier_trace(rsp, TPS("IRQ"), -1, rsp->barrier_sequence);
- rdp->barrier_head.func = rcu_barrier_callback;
- debug_rcu_head_queue(&rdp->barrier_head);
- if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) {
- atomic_inc(&rsp->barrier_cpu_count);
- } else {
- debug_rcu_head_unqueue(&rdp->barrier_head);
- _rcu_barrier_trace(rsp, TPS("IRQNQ"), -1,
- rsp->barrier_sequence);
- }
- }
- /*
- * Orchestrate the specified type of RCU barrier, waiting for all
- * RCU callbacks of the specified type to complete.
- */
- static void _rcu_barrier(struct rcu_state *rsp)
- {
- int cpu;
- struct rcu_data *rdp;
- unsigned long s = rcu_seq_snap(&rsp->barrier_sequence);
- _rcu_barrier_trace(rsp, TPS("Begin"), -1, s);
- /* Take mutex to serialize concurrent rcu_barrier() requests. */
- mutex_lock(&rsp->barrier_mutex);
- /* Did someone else do our work for us? */
- if (rcu_seq_done(&rsp->barrier_sequence, s)) {
- _rcu_barrier_trace(rsp, TPS("EarlyExit"), -1,
- rsp->barrier_sequence);
- smp_mb(); /* caller's subsequent code after above check. */
- mutex_unlock(&rsp->barrier_mutex);
- return;
- }
- /* Mark the start of the barrier operation. */
- rcu_seq_start(&rsp->barrier_sequence);
- _rcu_barrier_trace(rsp, TPS("Inc1"), -1, rsp->barrier_sequence);
- /*
- * Initialize the count to one rather than to zero in order to
- * avoid a too-soon return to zero in case of a short grace period
- * (or preemption of this task). Exclude CPU-hotplug operations
- * to ensure that no offline CPU has callbacks queued.
- */
- init_completion(&rsp->barrier_completion);
- atomic_set(&rsp->barrier_cpu_count, 1);
- get_online_cpus();
- /*
- * Force each CPU with callbacks to register a new callback.
- * When that callback is invoked, we will know that all of the
- * corresponding CPU's preceding callbacks have been invoked.
- */
- for_each_possible_cpu(cpu) {
- if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
- continue;
- rdp = per_cpu_ptr(rsp->rda, cpu);
- if (rcu_is_nocb_cpu(cpu)) {
- if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
- _rcu_barrier_trace(rsp, TPS("OfflineNoCB"), cpu,
- rsp->barrier_sequence);
- } else {
- _rcu_barrier_trace(rsp, TPS("OnlineNoCB"), cpu,
- rsp->barrier_sequence);
- smp_mb__before_atomic();
- atomic_inc(&rsp->barrier_cpu_count);
- __call_rcu(&rdp->barrier_head,
- rcu_barrier_callback, rsp, cpu, 0);
- }
- } else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
- _rcu_barrier_trace(rsp, TPS("OnlineQ"), cpu,
- rsp->barrier_sequence);
- smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
- } else {
- _rcu_barrier_trace(rsp, TPS("OnlineNQ"), cpu,
- rsp->barrier_sequence);
- }
- }
- put_online_cpus();
- /*
- * Now that we have an rcu_barrier_callback() callback on each
- * CPU, and thus each counted, remove the initial count.
- */
- if (atomic_dec_and_test(&rsp->barrier_cpu_count))
- complete(&rsp->barrier_completion);
- /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
- wait_for_completion(&rsp->barrier_completion);
- /* Mark the end of the barrier operation. */
- _rcu_barrier_trace(rsp, TPS("Inc2"), -1, rsp->barrier_sequence);
- rcu_seq_end(&rsp->barrier_sequence);
- /* Other rcu_barrier() invocations can now safely proceed. */
- mutex_unlock(&rsp->barrier_mutex);
- }
- /**
- * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
- */
- void rcu_barrier_bh(void)
- {
- _rcu_barrier(&rcu_bh_state);
- }
- EXPORT_SYMBOL_GPL(rcu_barrier_bh);
- /**
- * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
- */
- void rcu_barrier_sched(void)
- {
- _rcu_barrier(&rcu_sched_state);
- }
- EXPORT_SYMBOL_GPL(rcu_barrier_sched);
- /*
- * Propagate ->qsinitmask bits up the rcu_node tree to account for the
- * first CPU in a given leaf rcu_node structure coming online. The caller
- * must hold the corresponding leaf rcu_node ->lock with interrrupts
- * disabled.
- */
- static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
- {
- long mask;
- long oldmask;
- struct rcu_node *rnp = rnp_leaf;
- raw_lockdep_assert_held_rcu_node(rnp_leaf);
- WARN_ON_ONCE(rnp->wait_blkd_tasks);
- for (;;) {
- mask = rnp->grpmask;
- rnp = rnp->parent;
- if (rnp == NULL)
- return;
- raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
- oldmask = rnp->qsmaskinit;
- rnp->qsmaskinit |= mask;
- raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
- if (oldmask)
- return;
- }
- }
- /*
- * Do boot-time initialization of a CPU's per-CPU RCU data.
- */
- static void __init
- rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
- {
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- /* Set up local state, ensuring consistent view of global state. */
- rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
- rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
- WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != 1);
- WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
- rdp->rcu_ofl_gp_seq = rsp->gp_seq;
- rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
- rdp->rcu_onl_gp_seq = rsp->gp_seq;
- rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
- rdp->cpu = cpu;
- rdp->rsp = rsp;
- rcu_boot_init_nocb_percpu_data(rdp);
- }
- /*
- * Initialize a CPU's per-CPU RCU data. Note that only one online or
- * offline event can be happening at a given time. Note also that we can
- * accept some slop in the rsp->gp_seq access due to the fact that this
- * CPU cannot possibly have any RCU callbacks in flight yet.
- */
- static void
- rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
- {
- unsigned long flags;
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- struct rcu_node *rnp = rcu_get_root(rsp);
- /* Set up local state, ensuring consistent view of global state. */
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- rdp->qlen_last_fqs_check = 0;
- rdp->n_force_qs_snap = rsp->n_force_qs;
- rdp->blimit = blimit;
- if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
- !init_nocb_callback_list(rdp))
- rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
- rdp->dynticks->dynticks_nesting = 1; /* CPU not up, no tearing. */
- rcu_dynticks_eqs_online();
- raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
- /*
- * Add CPU to leaf rcu_node pending-online bitmask. Any needed
- * propagation up the rcu_node tree will happen at the beginning
- * of the next grace period.
- */
- rnp = rdp->mynode;
- raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
- rdp->beenonline = true; /* We have now been online. */
- rdp->gp_seq = rnp->gp_seq;
- rdp->gp_seq_needed = rnp->gp_seq;
- rdp->cpu_no_qs.b.norm = true;
- rdp->rcu_qs_ctr_snap = per_cpu(rcu_dynticks.rcu_qs_ctr, cpu);
- rdp->core_needs_qs = false;
- rdp->rcu_iw_pending = false;
- rdp->rcu_iw_gp_seq = rnp->gp_seq - 1;
- trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("cpuonl"));
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- /*
- * Invoked early in the CPU-online process, when pretty much all
- * services are available. The incoming CPU is not present.
- */
- int rcutree_prepare_cpu(unsigned int cpu)
- {
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp)
- rcu_init_percpu_data(cpu, rsp);
- rcu_prepare_kthreads(cpu);
- rcu_spawn_all_nocb_kthreads(cpu);
- return 0;
- }
- /*
- * Update RCU priority boot kthread affinity for CPU-hotplug changes.
- */
- static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
- {
- struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
- rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
- }
- /*
- * Near the end of the CPU-online process. Pretty much all services
- * enabled, and the CPU is now very much alive.
- */
- int rcutree_online_cpu(unsigned int cpu)
- {
- unsigned long flags;
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
- rnp = rdp->mynode;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- rnp->ffmask |= rdp->grpmask;
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- if (IS_ENABLED(CONFIG_TREE_SRCU))
- srcu_online_cpu(cpu);
- if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
- return 0; /* Too early in boot for scheduler work. */
- sync_sched_exp_online_cleanup(cpu);
- rcutree_affinity_setting(cpu, -1);
- return 0;
- }
- /*
- * Near the beginning of the process. The CPU is still very much alive
- * with pretty much all services enabled.
- */
- int rcutree_offline_cpu(unsigned int cpu)
- {
- unsigned long flags;
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
- rnp = rdp->mynode;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- rnp->ffmask &= ~rdp->grpmask;
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- rcutree_affinity_setting(cpu, cpu);
- if (IS_ENABLED(CONFIG_TREE_SRCU))
- srcu_offline_cpu(cpu);
- return 0;
- }
- /*
- * Near the end of the offline process. We do only tracing here.
- */
- int rcutree_dying_cpu(unsigned int cpu)
- {
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp)
- rcu_cleanup_dying_cpu(rsp);
- return 0;
- }
- /*
- * The outgoing CPU is gone and we are running elsewhere.
- */
- int rcutree_dead_cpu(unsigned int cpu)
- {
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp) {
- rcu_cleanup_dead_cpu(cpu, rsp);
- do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
- }
- return 0;
- }
- static DEFINE_PER_CPU(int, rcu_cpu_started);
- /*
- * Mark the specified CPU as being online so that subsequent grace periods
- * (both expedited and normal) will wait on it. Note that this means that
- * incoming CPUs are not allowed to use RCU read-side critical sections
- * until this function is called. Failing to observe this restriction
- * will result in lockdep splats.
- *
- * Note that this function is special in that it is invoked directly
- * from the incoming CPU rather than from the cpuhp_step mechanism.
- * This is because this function must be invoked at a precise location.
- */
- void rcu_cpu_starting(unsigned int cpu)
- {
- unsigned long flags;
- unsigned long mask;
- int nbits;
- unsigned long oldmask;
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- struct rcu_state *rsp;
- if (per_cpu(rcu_cpu_started, cpu))
- return;
- per_cpu(rcu_cpu_started, cpu) = 1;
- for_each_rcu_flavor(rsp) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
- rnp = rdp->mynode;
- mask = rdp->grpmask;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- rnp->qsmaskinitnext |= mask;
- oldmask = rnp->expmaskinitnext;
- rnp->expmaskinitnext |= mask;
- oldmask ^= rnp->expmaskinitnext;
- nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
- /* Allow lockless access for expedited grace periods. */
- smp_store_release(&rsp->ncpus, rsp->ncpus + nbits); /* ^^^ */
- rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
- rdp->rcu_onl_gp_seq = READ_ONCE(rsp->gp_seq);
- rdp->rcu_onl_gp_flags = READ_ONCE(rsp->gp_flags);
- if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */
- /* Report QS -after- changing ->qsmaskinitnext! */
- rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
- } else {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- }
- smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
- }
- #ifdef CONFIG_HOTPLUG_CPU
- /*
- * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
- * function. We now remove it from the rcu_node tree's ->qsmaskinitnext
- * bit masks.
- */
- static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
- {
- unsigned long flags;
- unsigned long mask;
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
- /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
- mask = rdp->grpmask;
- spin_lock(&rsp->ofl_lock);
- raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
- rdp->rcu_ofl_gp_seq = READ_ONCE(rsp->gp_seq);
- rdp->rcu_ofl_gp_flags = READ_ONCE(rsp->gp_flags);
- if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
- /* Report quiescent state -before- changing ->qsmaskinitnext! */
- rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- }
- rnp->qsmaskinitnext &= ~mask;
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- spin_unlock(&rsp->ofl_lock);
- }
- /*
- * The outgoing function has no further need of RCU, so remove it from
- * the list of CPUs that RCU must track.
- *
- * Note that this function is special in that it is invoked directly
- * from the outgoing CPU rather than from the cpuhp_step mechanism.
- * This is because this function must be invoked at a precise location.
- */
- void rcu_report_dead(unsigned int cpu)
- {
- struct rcu_state *rsp;
- /* QS for any half-done expedited RCU-sched GP. */
- preempt_disable();
- rcu_report_exp_rdp(&rcu_sched_state,
- this_cpu_ptr(rcu_sched_state.rda), true);
- preempt_enable();
- for_each_rcu_flavor(rsp)
- rcu_cleanup_dying_idle_cpu(cpu, rsp);
- per_cpu(rcu_cpu_started, cpu) = 0;
- }
- /* Migrate the dead CPU's callbacks to the current CPU. */
- static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp)
- {
- unsigned long flags;
- struct rcu_data *my_rdp;
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
- bool needwake;
- if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist))
- return; /* No callbacks to migrate. */
- local_irq_save(flags);
- my_rdp = this_cpu_ptr(rsp->rda);
- if (rcu_nocb_adopt_orphan_cbs(my_rdp, rdp, flags)) {
- local_irq_restore(flags);
- return;
- }
- raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
- /* Leverage recent GPs and set GP for new callbacks. */
- needwake = rcu_advance_cbs(rsp, rnp_root, rdp) ||
- rcu_advance_cbs(rsp, rnp_root, my_rdp);
- rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
- WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
- !rcu_segcblist_n_cbs(&my_rdp->cblist));
- raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags);
- if (needwake)
- rcu_gp_kthread_wake(rsp);
- WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
- !rcu_segcblist_empty(&rdp->cblist),
- "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
- cpu, rcu_segcblist_n_cbs(&rdp->cblist),
- rcu_segcblist_first_cb(&rdp->cblist));
- }
- /*
- * The outgoing CPU has just passed through the dying-idle state,
- * and we are being invoked from the CPU that was IPIed to continue the
- * offline operation. We need to migrate the outgoing CPU's callbacks.
- */
- void rcutree_migrate_callbacks(int cpu)
- {
- struct rcu_state *rsp;
- for_each_rcu_flavor(rsp)
- rcu_migrate_callbacks(cpu, rsp);
- }
- #endif
- /*
- * On non-huge systems, use expedited RCU grace periods to make suspend
- * and hibernation run faster.
- */
- static int rcu_pm_notify(struct notifier_block *self,
- unsigned long action, void *hcpu)
- {
- switch (action) {
- case PM_HIBERNATION_PREPARE:
- case PM_SUSPEND_PREPARE:
- if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
- rcu_expedite_gp();
- break;
- case PM_POST_HIBERNATION:
- case PM_POST_SUSPEND:
- if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
- rcu_unexpedite_gp();
- break;
- default:
- break;
- }
- return NOTIFY_OK;
- }
- /*
- * Spawn the kthreads that handle each RCU flavor's grace periods.
- */
- static int __init rcu_spawn_gp_kthread(void)
- {
- unsigned long flags;
- int kthread_prio_in = kthread_prio;
- struct rcu_node *rnp;
- struct rcu_state *rsp;
- struct sched_param sp;
- struct task_struct *t;
- /* Force priority into range. */
- if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
- && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
- kthread_prio = 2;
- else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
- kthread_prio = 1;
- else if (kthread_prio < 0)
- kthread_prio = 0;
- else if (kthread_prio > 99)
- kthread_prio = 99;
- if (kthread_prio != kthread_prio_in)
- pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
- kthread_prio, kthread_prio_in);
- rcu_scheduler_fully_active = 1;
- for_each_rcu_flavor(rsp) {
- t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
- BUG_ON(IS_ERR(t));
- rnp = rcu_get_root(rsp);
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- rsp->gp_kthread = t;
- if (kthread_prio) {
- sp.sched_priority = kthread_prio;
- sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
- }
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- wake_up_process(t);
- }
- rcu_spawn_nocb_kthreads();
- rcu_spawn_boost_kthreads();
- return 0;
- }
- early_initcall(rcu_spawn_gp_kthread);
- /*
- * This function is invoked towards the end of the scheduler's
- * initialization process. Before this is called, the idle task might
- * contain synchronous grace-period primitives (during which time, this idle
- * task is booting the system, and such primitives are no-ops). After this
- * function is called, any synchronous grace-period primitives are run as
- * expedited, with the requesting task driving the grace period forward.
- * A later core_initcall() rcu_set_runtime_mode() will switch to full
- * runtime RCU functionality.
- */
- void rcu_scheduler_starting(void)
- {
- WARN_ON(num_online_cpus() != 1);
- WARN_ON(nr_context_switches() > 0);
- rcu_test_sync_prims();
- rcu_scheduler_active = RCU_SCHEDULER_INIT;
- rcu_test_sync_prims();
- }
- /*
- * Helper function for rcu_init() that initializes one rcu_state structure.
- */
- static void __init rcu_init_one(struct rcu_state *rsp)
- {
- static const char * const buf[] = RCU_NODE_NAME_INIT;
- static const char * const fqs[] = RCU_FQS_NAME_INIT;
- static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
- static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
- int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
- int cpustride = 1;
- int i;
- int j;
- struct rcu_node *rnp;
- BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
- /* Silence gcc 4.8 false positive about array index out of range. */
- if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
- panic("rcu_init_one: rcu_num_lvls out of range");
- /* Initialize the level-tracking arrays. */
- for (i = 1; i < rcu_num_lvls; i++)
- rsp->level[i] = rsp->level[i - 1] + num_rcu_lvl[i - 1];
- rcu_init_levelspread(levelspread, num_rcu_lvl);
- /* Initialize the elements themselves, starting from the leaves. */
- for (i = rcu_num_lvls - 1; i >= 0; i--) {
- cpustride *= levelspread[i];
- rnp = rsp->level[i];
- for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
- raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
- lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
- &rcu_node_class[i], buf[i]);
- raw_spin_lock_init(&rnp->fqslock);
- lockdep_set_class_and_name(&rnp->fqslock,
- &rcu_fqs_class[i], fqs[i]);
- rnp->gp_seq = rsp->gp_seq;
- rnp->gp_seq_needed = rsp->gp_seq;
- rnp->completedqs = rsp->gp_seq;
- rnp->qsmask = 0;
- rnp->qsmaskinit = 0;
- rnp->grplo = j * cpustride;
- rnp->grphi = (j + 1) * cpustride - 1;
- if (rnp->grphi >= nr_cpu_ids)
- rnp->grphi = nr_cpu_ids - 1;
- if (i == 0) {
- rnp->grpnum = 0;
- rnp->grpmask = 0;
- rnp->parent = NULL;
- } else {
- rnp->grpnum = j % levelspread[i - 1];
- rnp->grpmask = 1UL << rnp->grpnum;
- rnp->parent = rsp->level[i - 1] +
- j / levelspread[i - 1];
- }
- rnp->level = i;
- INIT_LIST_HEAD(&rnp->blkd_tasks);
- rcu_init_one_nocb(rnp);
- init_waitqueue_head(&rnp->exp_wq[0]);
- init_waitqueue_head(&rnp->exp_wq[1]);
- init_waitqueue_head(&rnp->exp_wq[2]);
- init_waitqueue_head(&rnp->exp_wq[3]);
- spin_lock_init(&rnp->exp_lock);
- }
- }
- init_swait_queue_head(&rsp->gp_wq);
- init_swait_queue_head(&rsp->expedited_wq);
- rnp = rcu_first_leaf_node(rsp);
- for_each_possible_cpu(i) {
- while (i > rnp->grphi)
- rnp++;
- per_cpu_ptr(rsp->rda, i)->mynode = rnp;
- rcu_boot_init_percpu_data(i, rsp);
- }
- list_add(&rsp->flavors, &rcu_struct_flavors);
- }
- /*
- * Compute the rcu_node tree geometry from kernel parameters. This cannot
- * replace the definitions in tree.h because those are needed to size
- * the ->node array in the rcu_state structure.
- */
- static void __init rcu_init_geometry(void)
- {
- ulong d;
- int i;
- int rcu_capacity[RCU_NUM_LVLS];
- /*
- * Initialize any unspecified boot parameters.
- * The default values of jiffies_till_first_fqs and
- * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
- * value, which is a function of HZ, then adding one for each
- * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
- */
- d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
- if (jiffies_till_first_fqs == ULONG_MAX)
- jiffies_till_first_fqs = d;
- if (jiffies_till_next_fqs == ULONG_MAX)
- jiffies_till_next_fqs = d;
- /* If the compile-time values are accurate, just leave. */
- if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
- nr_cpu_ids == NR_CPUS)
- return;
- pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
- rcu_fanout_leaf, nr_cpu_ids);
- /*
- * The boot-time rcu_fanout_leaf parameter must be at least two
- * and cannot exceed the number of bits in the rcu_node masks.
- * Complain and fall back to the compile-time values if this
- * limit is exceeded.
- */
- if (rcu_fanout_leaf < 2 ||
- rcu_fanout_leaf > sizeof(unsigned long) * 8) {
- rcu_fanout_leaf = RCU_FANOUT_LEAF;
- WARN_ON(1);
- return;
- }
- /*
- * Compute number of nodes that can be handled an rcu_node tree
- * with the given number of levels.
- */
- rcu_capacity[0] = rcu_fanout_leaf;
- for (i = 1; i < RCU_NUM_LVLS; i++)
- rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
- /*
- * The tree must be able to accommodate the configured number of CPUs.
- * If this limit is exceeded, fall back to the compile-time values.
- */
- if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
- rcu_fanout_leaf = RCU_FANOUT_LEAF;
- WARN_ON(1);
- return;
- }
- /* Calculate the number of levels in the tree. */
- for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
- }
- rcu_num_lvls = i + 1;
- /* Calculate the number of rcu_nodes at each level of the tree. */
- for (i = 0; i < rcu_num_lvls; i++) {
- int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
- num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
- }
- /* Calculate the total number of rcu_node structures. */
- rcu_num_nodes = 0;
- for (i = 0; i < rcu_num_lvls; i++)
- rcu_num_nodes += num_rcu_lvl[i];
- }
- /*
- * Dump out the structure of the rcu_node combining tree associated
- * with the rcu_state structure referenced by rsp.
- */
- static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
- {
- int level = 0;
- struct rcu_node *rnp;
- pr_info("rcu_node tree layout dump\n");
- pr_info(" ");
- rcu_for_each_node_breadth_first(rsp, rnp) {
- if (rnp->level != level) {
- pr_cont("\n");
- pr_info(" ");
- level = rnp->level;
- }
- pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
- }
- pr_cont("\n");
- }
- struct workqueue_struct *rcu_gp_wq;
- struct workqueue_struct *rcu_par_gp_wq;
- void __init rcu_init(void)
- {
- int cpu;
- rcu_early_boot_tests();
- rcu_bootup_announce();
- rcu_init_geometry();
- rcu_init_one(&rcu_bh_state);
- rcu_init_one(&rcu_sched_state);
- if (dump_tree)
- rcu_dump_rcu_node_tree(&rcu_sched_state);
- __rcu_init_preempt();
- open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
- /*
- * We don't need protection against CPU-hotplug here because
- * this is called early in boot, before either interrupts
- * or the scheduler are operational.
- */
- pm_notifier(rcu_pm_notify, 0);
- for_each_online_cpu(cpu) {
- rcutree_prepare_cpu(cpu);
- rcu_cpu_starting(cpu);
- rcutree_online_cpu(cpu);
- }
- /* Create workqueue for expedited GPs and for Tree SRCU. */
- rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
- WARN_ON(!rcu_gp_wq);
- rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
- WARN_ON(!rcu_par_gp_wq);
- }
- #include "tree_exp.h"
- #include "tree_plugin.h"
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