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Diffstat (limited to '')
| -rw-r--r-- | kernel/rcu/tree_exp.h | 870 |
1 files changed, 870 insertions, 0 deletions
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h new file mode 100644 index 000000000..07a284a18 --- /dev/null +++ b/kernel/rcu/tree_exp.h @@ -0,0 +1,870 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * RCU expedited grace periods + * + * Copyright IBM Corporation, 2016 + * + * Authors: Paul E. McKenney <paulmck@linux.ibm.com> + */ + +#include <linux/lockdep.h> + +static void rcu_exp_handler(void *unused); +static int rcu_print_task_exp_stall(struct rcu_node *rnp); + +/* + * Record the start of an expedited grace period. + */ +static void rcu_exp_gp_seq_start(void) +{ + rcu_seq_start(&rcu_state.expedited_sequence); +} + +/* + * Return the value that the expedited-grace-period counter will have + * at the end of the current grace period. + */ +static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void) +{ + return rcu_seq_endval(&rcu_state.expedited_sequence); +} + +/* + * Record the end of an expedited grace period. + */ +static void rcu_exp_gp_seq_end(void) +{ + rcu_seq_end(&rcu_state.expedited_sequence); + smp_mb(); /* Ensure that consecutive grace periods serialize. */ +} + +/* + * Take a snapshot of the expedited-grace-period counter, which is the + * earliest value that will indicate that a full grace period has + * elapsed since the current time. + */ +static unsigned long rcu_exp_gp_seq_snap(void) +{ + unsigned long s; + + smp_mb(); /* Caller's modifications seen first by other CPUs. */ + s = rcu_seq_snap(&rcu_state.expedited_sequence); + trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap")); + return s; +} + +/* + * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true + * if a full expedited grace period has elapsed since that snapshot + * was taken. + */ +static bool rcu_exp_gp_seq_done(unsigned long s) +{ + return rcu_seq_done(&rcu_state.expedited_sequence, s); +} + +/* + * Reset the ->expmaskinit values in the rcu_node tree to reflect any + * recent CPU-online activity. Note that these masks are not cleared + * when CPUs go offline, so they reflect the union of all CPUs that have + * ever been online. This means that this function normally takes its + * no-work-to-do fastpath. + */ +static void sync_exp_reset_tree_hotplug(void) +{ + bool done; + unsigned long flags; + unsigned long mask; + unsigned long oldmask; + int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */ + struct rcu_node *rnp; + struct rcu_node *rnp_up; + + /* If no new CPUs onlined since last time, nothing to do. */ + if (likely(ncpus == rcu_state.ncpus_snap)) + return; + rcu_state.ncpus_snap = ncpus; + + /* + * Each pass through the following loop propagates newly onlined + * CPUs for the current rcu_node structure up the rcu_node tree. + */ + rcu_for_each_leaf_node(rnp) { + raw_spin_lock_irqsave_rcu_node(rnp, flags); + if (rnp->expmaskinit == rnp->expmaskinitnext) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + continue; /* No new CPUs, nothing to do. */ + } + + /* Update this node's mask, track old value for propagation. */ + oldmask = rnp->expmaskinit; + rnp->expmaskinit = rnp->expmaskinitnext; + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + + /* If was already nonzero, nothing to propagate. */ + if (oldmask) + continue; + + /* Propagate the new CPU up the tree. */ + mask = rnp->grpmask; + rnp_up = rnp->parent; + done = false; + while (rnp_up) { + raw_spin_lock_irqsave_rcu_node(rnp_up, flags); + if (rnp_up->expmaskinit) + done = true; + rnp_up->expmaskinit |= mask; + raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags); + if (done) + break; + mask = rnp_up->grpmask; + rnp_up = rnp_up->parent; + } + } +} + +/* + * Reset the ->expmask values in the rcu_node tree in preparation for + * a new expedited grace period. + */ +static void __maybe_unused sync_exp_reset_tree(void) +{ + unsigned long flags; + struct rcu_node *rnp; + + sync_exp_reset_tree_hotplug(); + rcu_for_each_node_breadth_first(rnp) { + raw_spin_lock_irqsave_rcu_node(rnp, flags); + WARN_ON_ONCE(rnp->expmask); + WRITE_ONCE(rnp->expmask, rnp->expmaskinit); + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + } +} + +/* + * Return non-zero if there is no RCU expedited grace period in progress + * for the specified rcu_node structure, in other words, if all CPUs and + * tasks covered by the specified rcu_node structure have done their bit + * for the current expedited grace period. + */ +static bool sync_rcu_exp_done(struct rcu_node *rnp) +{ + raw_lockdep_assert_held_rcu_node(rnp); + return READ_ONCE(rnp->exp_tasks) == NULL && + READ_ONCE(rnp->expmask) == 0; +} + +/* + * Like sync_rcu_exp_done(), but where the caller does not hold the + * rcu_node's ->lock. + */ +static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp) +{ + unsigned long flags; + bool ret; + + raw_spin_lock_irqsave_rcu_node(rnp, flags); + ret = sync_rcu_exp_done(rnp); + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + + return ret; +} + + +/* + * Report the exit from RCU read-side critical section for the last task + * that queued itself during or before the current expedited preemptible-RCU + * grace period. This event is reported either to the rcu_node structure on + * which the task was queued or to one of that rcu_node structure's ancestors, + * recursively up the tree. (Calm down, calm down, we do the recursion + * iteratively!) + */ +static void __rcu_report_exp_rnp(struct rcu_node *rnp, + bool wake, unsigned long flags) + __releases(rnp->lock) +{ + unsigned long mask; + + raw_lockdep_assert_held_rcu_node(rnp); + for (;;) { + if (!sync_rcu_exp_done(rnp)) { + if (!rnp->expmask) + rcu_initiate_boost(rnp, flags); + else + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + break; + } + if (rnp->parent == NULL) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + if (wake) { + smp_mb(); /* EGP done before wake_up(). */ + swake_up_one(&rcu_state.expedited_wq); + } + break; + } + mask = rnp->grpmask; + raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */ + rnp = rnp->parent; + raw_spin_lock_rcu_node(rnp); /* irqs already disabled */ + WARN_ON_ONCE(!(rnp->expmask & mask)); + WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask); + } +} + +/* + * Report expedited quiescent state for specified node. This is a + * lock-acquisition wrapper function for __rcu_report_exp_rnp(). + */ +static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake) +{ + unsigned long flags; + + raw_spin_lock_irqsave_rcu_node(rnp, flags); + __rcu_report_exp_rnp(rnp, wake, flags); +} + +/* + * Report expedited quiescent state for multiple CPUs, all covered by the + * specified leaf rcu_node structure. + */ +static void rcu_report_exp_cpu_mult(struct rcu_node *rnp, + unsigned long mask, bool wake) +{ + int cpu; + unsigned long flags; + struct rcu_data *rdp; + + raw_spin_lock_irqsave_rcu_node(rnp, flags); + if (!(rnp->expmask & mask)) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return; + } + WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask); + for_each_leaf_node_cpu_mask(rnp, cpu, mask) { + rdp = per_cpu_ptr(&rcu_data, cpu); + if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp) + continue; + rdp->rcu_forced_tick_exp = false; + tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP); + } + __rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */ +} + +/* + * Report expedited quiescent state for specified rcu_data (CPU). + */ +static void rcu_report_exp_rdp(struct rcu_data *rdp) +{ + WRITE_ONCE(rdp->exp_deferred_qs, false); + rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true); +} + +/* Common code for work-done checking. */ +static bool sync_exp_work_done(unsigned long s) +{ + if (rcu_exp_gp_seq_done(s)) { + trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done")); + smp_mb(); /* Ensure test happens before caller kfree(). */ + return true; + } + return false; +} + +/* + * Funnel-lock acquisition for expedited grace periods. Returns true + * if some other task completed an expedited grace period that this task + * can piggy-back on, and with no mutex held. Otherwise, returns false + * with the mutex held, indicating that the caller must actually do the + * expedited grace period. + */ +static bool exp_funnel_lock(unsigned long s) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id()); + struct rcu_node *rnp = rdp->mynode; + struct rcu_node *rnp_root = rcu_get_root(); + + /* Low-contention fastpath. */ + if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) && + (rnp == rnp_root || + ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) && + mutex_trylock(&rcu_state.exp_mutex)) + goto fastpath; + + /* + * Each pass through the following loop works its way up + * the rcu_node tree, returning if others have done the work or + * otherwise falls through to acquire ->exp_mutex. The mapping + * from CPU to rcu_node structure can be inexact, as it is just + * promoting locality and is not strictly needed for correctness. + */ + for (; rnp != NULL; rnp = rnp->parent) { + if (sync_exp_work_done(s)) + return true; + + /* Work not done, either wait here or go up. */ + spin_lock(&rnp->exp_lock); + if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) { + + /* Someone else doing GP, so wait for them. */ + spin_unlock(&rnp->exp_lock); + trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level, + rnp->grplo, rnp->grphi, + TPS("wait")); + wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3], + sync_exp_work_done(s)); + return true; + } + WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */ + spin_unlock(&rnp->exp_lock); + trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level, + rnp->grplo, rnp->grphi, TPS("nxtlvl")); + } + mutex_lock(&rcu_state.exp_mutex); +fastpath: + if (sync_exp_work_done(s)) { + mutex_unlock(&rcu_state.exp_mutex); + return true; + } + rcu_exp_gp_seq_start(); + trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start")); + return false; +} + +/* + * Select the CPUs within the specified rcu_node that the upcoming + * expedited grace period needs to wait for. + */ +static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) +{ + int cpu; + unsigned long flags; + unsigned long mask_ofl_test; + unsigned long mask_ofl_ipi; + int ret; + struct rcu_exp_work *rewp = + container_of(wp, struct rcu_exp_work, rew_work); + struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew); + + raw_spin_lock_irqsave_rcu_node(rnp, flags); + + /* Each pass checks a CPU for identity, offline, and idle. */ + mask_ofl_test = 0; + for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) { + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + unsigned long mask = rdp->grpmask; + int snap; + + if (raw_smp_processor_id() == cpu || + !(rnp->qsmaskinitnext & mask)) { + mask_ofl_test |= mask; + } else { + snap = rcu_dynticks_snap(rdp); + if (rcu_dynticks_in_eqs(snap)) + mask_ofl_test |= mask; + else + rdp->exp_dynticks_snap = snap; + } + } + mask_ofl_ipi = rnp->expmask & ~mask_ofl_test; + + /* + * Need to wait for any blocked tasks as well. Note that + * additional blocking tasks will also block the expedited GP + * until such time as the ->expmask bits are cleared. + */ + if (rcu_preempt_has_tasks(rnp)) + WRITE_ONCE(rnp->exp_tasks, rnp->blkd_tasks.next); + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + + /* IPI the remaining CPUs for expedited quiescent state. */ + for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) { + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + unsigned long mask = rdp->grpmask; + +retry_ipi: + if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) { + mask_ofl_test |= mask; + continue; + } + if (get_cpu() == cpu) { + mask_ofl_test |= mask; + put_cpu(); + continue; + } + ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); + put_cpu(); + /* The CPU will report the QS in response to the IPI. */ + if (!ret) + continue; + + /* Failed, raced with CPU hotplug operation. */ + raw_spin_lock_irqsave_rcu_node(rnp, flags); + if ((rnp->qsmaskinitnext & mask) && + (rnp->expmask & mask)) { + /* Online, so delay for a bit and try again. */ + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl")); + schedule_timeout_idle(1); + goto retry_ipi; + } + /* CPU really is offline, so we must report its QS. */ + if (rnp->expmask & mask) + mask_ofl_test |= mask; + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + } + /* Report quiescent states for those that went offline. */ + if (mask_ofl_test) + rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false); +} + +/* + * Select the nodes that the upcoming expedited grace period needs + * to wait for. + */ +static void sync_rcu_exp_select_cpus(void) +{ + int cpu; + struct rcu_node *rnp; + + trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset")); + sync_exp_reset_tree(); + trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select")); + + /* Schedule work for each leaf rcu_node structure. */ + rcu_for_each_leaf_node(rnp) { + rnp->exp_need_flush = false; + if (!READ_ONCE(rnp->expmask)) + continue; /* Avoid early boot non-existent wq. */ + if (!READ_ONCE(rcu_par_gp_wq) || + rcu_scheduler_active != RCU_SCHEDULER_RUNNING || + rcu_is_last_leaf_node(rnp)) { + /* No workqueues yet or last leaf, do direct call. */ + sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work); + continue; + } + INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus); + cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1); + /* If all offline, queue the work on an unbound CPU. */ + if (unlikely(cpu > rnp->grphi - rnp->grplo)) + cpu = WORK_CPU_UNBOUND; + else + cpu += rnp->grplo; + queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work); + rnp->exp_need_flush = true; + } + + /* Wait for workqueue jobs (if any) to complete. */ + rcu_for_each_leaf_node(rnp) + if (rnp->exp_need_flush) + flush_work(&rnp->rew.rew_work); +} + +/* + * Wait for the expedited grace period to elapse, within time limit. + * If the time limit is exceeded without the grace period elapsing, + * return false, otherwise return true. + */ +static bool synchronize_rcu_expedited_wait_once(long tlimit) +{ + int t; + struct rcu_node *rnp_root = rcu_get_root(); + + t = swait_event_timeout_exclusive(rcu_state.expedited_wq, + sync_rcu_exp_done_unlocked(rnp_root), + tlimit); + // Workqueues should not be signaled. + if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root)) + return true; + WARN_ON(t < 0); /* workqueues should not be signaled. */ + return false; +} + +/* + * Wait for the expedited grace period to elapse, issuing any needed + * RCU CPU stall warnings along the way. + */ +static void synchronize_rcu_expedited_wait(void) +{ + int cpu; + unsigned long j; + unsigned long jiffies_stall; + unsigned long jiffies_start; + unsigned long mask; + int ndetected; + struct rcu_data *rdp; + struct rcu_node *rnp; + struct rcu_node *rnp_root = rcu_get_root(); + + trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait")); + jiffies_stall = rcu_jiffies_till_stall_check(); + jiffies_start = jiffies; + if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) { + if (synchronize_rcu_expedited_wait_once(1)) + return; + rcu_for_each_leaf_node(rnp) { + for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) { + rdp = per_cpu_ptr(&rcu_data, cpu); + if (rdp->rcu_forced_tick_exp) + continue; + rdp->rcu_forced_tick_exp = true; + preempt_disable(); + if (cpu_online(cpu)) + tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP); + preempt_enable(); + } + } + j = READ_ONCE(jiffies_till_first_fqs); + if (synchronize_rcu_expedited_wait_once(j + HZ)) + return; + WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)); + } + + for (;;) { + if (synchronize_rcu_expedited_wait_once(jiffies_stall)) + return; + if (rcu_stall_is_suppressed()) + continue; + panic_on_rcu_stall(); + pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {", + rcu_state.name); + ndetected = 0; + rcu_for_each_leaf_node(rnp) { + ndetected += rcu_print_task_exp_stall(rnp); + for_each_leaf_node_possible_cpu(rnp, cpu) { + struct rcu_data *rdp; + + mask = leaf_node_cpu_bit(rnp, cpu); + if (!(READ_ONCE(rnp->expmask) & mask)) + continue; + ndetected++; + rdp = per_cpu_ptr(&rcu_data, cpu); + pr_cont(" %d-%c%c%c", cpu, + "O."[!!cpu_online(cpu)], + "o."[!!(rdp->grpmask & rnp->expmaskinit)], + "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]); + } + } + pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n", + jiffies - jiffies_start, rcu_state.expedited_sequence, + data_race(rnp_root->expmask), + ".T"[!!data_race(rnp_root->exp_tasks)]); + if (ndetected) { + pr_err("blocking rcu_node structures:"); + rcu_for_each_node_breadth_first(rnp) { + if (rnp == rnp_root) + continue; /* printed unconditionally */ + if (sync_rcu_exp_done_unlocked(rnp)) + continue; + pr_cont(" l=%u:%d-%d:%#lx/%c", + rnp->level, rnp->grplo, rnp->grphi, + data_race(rnp->expmask), + ".T"[!!data_race(rnp->exp_tasks)]); + } + pr_cont("\n"); + } + rcu_for_each_leaf_node(rnp) { + for_each_leaf_node_possible_cpu(rnp, cpu) { + mask = leaf_node_cpu_bit(rnp, cpu); + if (!(READ_ONCE(rnp->expmask) & mask)) + continue; + preempt_disable(); // For smp_processor_id() in dump_cpu_task(). + dump_cpu_task(cpu); + preempt_enable(); + } + } + jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3; + } +} + +/* + * Wait for the current expedited grace period to complete, and then + * wake up everyone who piggybacked on the just-completed expedited + * grace period. Also update all the ->exp_seq_rq counters as needed + * in order to avoid counter-wrap problems. + */ +static void rcu_exp_wait_wake(unsigned long s) +{ + struct rcu_node *rnp; + + synchronize_rcu_expedited_wait(); + + // Switch over to wakeup mode, allowing the next GP to proceed. + // End the previous grace period only after acquiring the mutex + // to ensure that only one GP runs concurrently with wakeups. + mutex_lock(&rcu_state.exp_wake_mutex); + rcu_exp_gp_seq_end(); + trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end")); + + rcu_for_each_node_breadth_first(rnp) { + if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) { + spin_lock(&rnp->exp_lock); + /* Recheck, avoid hang in case someone just arrived. */ + if (ULONG_CMP_LT(rnp->exp_seq_rq, s)) + WRITE_ONCE(rnp->exp_seq_rq, s); + spin_unlock(&rnp->exp_lock); + } + smp_mb(); /* All above changes before wakeup. */ + wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]); + } + trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake")); + mutex_unlock(&rcu_state.exp_wake_mutex); +} + +/* + * Common code to drive an expedited grace period forward, used by + * workqueues and mid-boot-time tasks. + */ +static void rcu_exp_sel_wait_wake(unsigned long s) +{ + /* Initialize the rcu_node tree in preparation for the wait. */ + sync_rcu_exp_select_cpus(); + + /* Wait and clean up, including waking everyone. */ + rcu_exp_wait_wake(s); +} + +/* + * Work-queue handler to drive an expedited grace period forward. + */ +static void wait_rcu_exp_gp(struct work_struct *wp) +{ + struct rcu_exp_work *rewp; + + rewp = container_of(wp, struct rcu_exp_work, rew_work); + rcu_exp_sel_wait_wake(rewp->rew_s); +} + +#ifdef CONFIG_PREEMPT_RCU + +/* + * Remote handler for smp_call_function_single(). If there is an + * RCU read-side critical section in effect, request that the + * next rcu_read_unlock() record the quiescent state up the + * ->expmask fields in the rcu_node tree. Otherwise, immediately + * report the quiescent state. + */ +static void rcu_exp_handler(void *unused) +{ + int depth = rcu_preempt_depth(); + unsigned long flags; + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + struct rcu_node *rnp = rdp->mynode; + struct task_struct *t = current; + + /* + * First, the common case of not being in an RCU read-side + * critical section. If also enabled or idle, immediately + * report the quiescent state, otherwise defer. + */ + if (!depth) { + if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || + rcu_dynticks_curr_cpu_in_eqs()) { + rcu_report_exp_rdp(rdp); + } else { + rdp->exp_deferred_qs = true; + set_tsk_need_resched(t); + set_preempt_need_resched(); + } + return; + } + + /* + * Second, the less-common case of being in an RCU read-side + * critical section. In this case we can count on a future + * rcu_read_unlock(). However, this rcu_read_unlock() might + * execute on some other CPU, but in that case there will be + * a future context switch. Either way, if the expedited + * grace period is still waiting on this CPU, set ->deferred_qs + * so that the eventual quiescent state will be reported. + * Note that there is a large group of race conditions that + * can have caused this quiescent state to already have been + * reported, so we really do need to check ->expmask. + */ + if (depth > 0) { + raw_spin_lock_irqsave_rcu_node(rnp, flags); + if (rnp->expmask & rdp->grpmask) { + rdp->exp_deferred_qs = true; + t->rcu_read_unlock_special.b.exp_hint = true; + } + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return; + } + + // Finally, negative nesting depth should not happen. + WARN_ON_ONCE(1); +} + +/* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */ +static void sync_sched_exp_online_cleanup(int cpu) +{ +} + +/* + * Scan the current list of tasks blocked within RCU read-side critical + * sections, printing out the tid of each that is blocking the current + * expedited grace period. + */ +static int rcu_print_task_exp_stall(struct rcu_node *rnp) +{ + unsigned long flags; + int ndetected = 0; + struct task_struct *t; + + raw_spin_lock_irqsave_rcu_node(rnp, flags); + if (!rnp->exp_tasks) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return 0; + } + t = list_entry(rnp->exp_tasks->prev, + struct task_struct, rcu_node_entry); + list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { + pr_cont(" P%d", t->pid); + ndetected++; + } + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return ndetected; +} + +#else /* #ifdef CONFIG_PREEMPT_RCU */ + +/* Request an expedited quiescent state. */ +static void rcu_exp_need_qs(void) +{ + __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true); + /* Store .exp before .rcu_urgent_qs. */ + smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true); + set_tsk_need_resched(current); + set_preempt_need_resched(); +} + +/* Invoked on each online non-idle CPU for expedited quiescent state. */ +static void rcu_exp_handler(void *unused) +{ + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + struct rcu_node *rnp = rdp->mynode; + + if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || + __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) + return; + if (rcu_is_cpu_rrupt_from_idle()) { + rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); + return; + } + rcu_exp_need_qs(); +} + +/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */ +static void sync_sched_exp_online_cleanup(int cpu) +{ + unsigned long flags; + int my_cpu; + struct rcu_data *rdp; + int ret; + struct rcu_node *rnp; + + rdp = per_cpu_ptr(&rcu_data, cpu); + rnp = rdp->mynode; + my_cpu = get_cpu(); + /* Quiescent state either not needed or already requested, leave. */ + if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || + rdp->cpu_no_qs.b.exp) { + put_cpu(); + return; + } + /* Quiescent state needed on current CPU, so set it up locally. */ + if (my_cpu == cpu) { + local_irq_save(flags); + rcu_exp_need_qs(); + local_irq_restore(flags); + put_cpu(); + return; + } + /* Quiescent state needed on some other CPU, send IPI. */ + ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); + put_cpu(); + WARN_ON_ONCE(ret); +} + +/* + * Because preemptible RCU does not exist, we never have to check for + * tasks blocked within RCU read-side critical sections that are + * blocking the current expedited grace period. + */ +static int rcu_print_task_exp_stall(struct rcu_node *rnp) +{ + return 0; +} + +#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ + +/** + * synchronize_rcu_expedited - Brute-force RCU grace period + * + * Wait for an RCU grace period, but expedite it. The basic idea is to + * IPI all non-idle non-nohz online CPUs. The IPI handler checks whether + * the CPU is in an RCU critical section, and if so, it sets a flag that + * causes the outermost rcu_read_unlock() to report the quiescent state + * for RCU-preempt or asks the scheduler for help for RCU-sched. On the + * other hand, if the CPU is not in an RCU read-side critical section, + * the IPI handler reports the quiescent state immediately. + * + * Although this is a great improvement over previous expedited + * implementations, it is still unfriendly to real-time workloads, so is + * thus not recommended for any sort of common-case code. In fact, if + * you are using synchronize_rcu_expedited() in a loop, please restructure + * your code to batch your updates, and then use a single synchronize_rcu() + * instead. + * + * This has the same semantics as (but is more brutal than) synchronize_rcu(). + */ +void synchronize_rcu_expedited(void) +{ + bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT); + struct rcu_exp_work rew; + struct rcu_node *rnp; + unsigned long s; + + 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_expedited() in RCU read-side critical section"); + + /* Is the state is such that the call is a grace period? */ + if (rcu_blocking_is_gp()) + return; + + /* If expedited grace periods are prohibited, fall back to normal. */ + if (rcu_gp_is_normal()) { + wait_rcu_gp(call_rcu); + return; + } + + /* Take a snapshot of the sequence number. */ + s = rcu_exp_gp_seq_snap(); + if (exp_funnel_lock(s)) + return; /* Someone else did our work for us. */ + + /* Ensure that load happens before action based on it. */ + if (unlikely(boottime)) { + /* Direct call during scheduler init and early_initcalls(). */ + rcu_exp_sel_wait_wake(s); + } else { + /* Marshall arguments & schedule the expedited grace period. */ + rew.rew_s = s; + INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp); + queue_work(rcu_gp_wq, &rew.rew_work); + } + + /* Wait for expedited grace period to complete. */ + rnp = rcu_get_root(); + wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3], + sync_exp_work_done(s)); + smp_mb(); /* Workqueue actions happen before return. */ + + /* Let the next expedited grace period start. */ + mutex_unlock(&rcu_state.exp_mutex); + + if (likely(!boottime)) + destroy_work_on_stack(&rew.rew_work); +} +EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |