40e69ac7d0
The print_cpu_stall_info_begin() and print_cpu_stall_info_end() print a single character each onto the console, and are a holdover from a time when RCU CPU stall warning messages could be abbreviated using a long-gone Kconfig option. This commit therefore adds these single characters to already-printed strings in the calling functions, and then eliminates both print_cpu_stall_info_begin() and print_cpu_stall_info_end(). Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
425 lines
12 KiB
C
425 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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/*
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* RCU CPU stall warnings for normal RCU grace periods
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*
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* Copyright IBM Corporation, 2019
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*
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* Author: Paul E. McKenney <paulmck@linux.ibm.com>
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*/
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/* panic() on RCU Stall sysctl. */
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int sysctl_panic_on_rcu_stall __read_mostly;
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#ifdef CONFIG_PROVE_RCU
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#define RCU_STALL_DELAY_DELTA (5 * HZ)
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#else
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#define RCU_STALL_DELAY_DELTA 0
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#endif
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int rcu_jiffies_till_stall_check(void)
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{
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int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
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/*
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* Limit check must be consistent with the Kconfig limits
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* for CONFIG_RCU_CPU_STALL_TIMEOUT.
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*/
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if (till_stall_check < 3) {
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WRITE_ONCE(rcu_cpu_stall_timeout, 3);
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till_stall_check = 3;
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} else if (till_stall_check > 300) {
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WRITE_ONCE(rcu_cpu_stall_timeout, 300);
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till_stall_check = 300;
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}
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return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
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}
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EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);
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void rcu_sysrq_start(void)
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{
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if (!rcu_cpu_stall_suppress)
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rcu_cpu_stall_suppress = 2;
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}
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void rcu_sysrq_end(void)
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{
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if (rcu_cpu_stall_suppress == 2)
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rcu_cpu_stall_suppress = 0;
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}
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static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
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{
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rcu_cpu_stall_suppress = 1;
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return NOTIFY_DONE;
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}
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static struct notifier_block rcu_panic_block = {
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.notifier_call = rcu_panic,
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};
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static int __init check_cpu_stall_init(void)
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{
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atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
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return 0;
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}
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early_initcall(check_cpu_stall_init);
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#ifdef CONFIG_PREEMPT
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/*
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* Dump detailed information for all tasks blocking the current RCU
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* grace period on the specified rcu_node structure.
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*/
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static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
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{
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unsigned long flags;
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struct task_struct *t;
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raw_spin_lock_irqsave_rcu_node(rnp, flags);
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if (!rcu_preempt_blocked_readers_cgp(rnp)) {
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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return;
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}
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t = list_entry(rnp->gp_tasks->prev,
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struct task_struct, rcu_node_entry);
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list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
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/*
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* We could be printing a lot while holding a spinlock.
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* Avoid triggering hard lockup.
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*/
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touch_nmi_watchdog();
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sched_show_task(t);
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}
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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}
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/*
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* Scan the current list of tasks blocked within RCU read-side critical
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* sections, printing out the tid of each.
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*/
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static int rcu_print_task_stall(struct rcu_node *rnp)
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{
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struct task_struct *t;
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int ndetected = 0;
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if (!rcu_preempt_blocked_readers_cgp(rnp))
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return 0;
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pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
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rnp->level, rnp->grplo, rnp->grphi);
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t = list_entry(rnp->gp_tasks->prev,
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struct task_struct, rcu_node_entry);
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list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
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pr_cont(" P%d", t->pid);
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ndetected++;
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}
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pr_cont("\n");
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return ndetected;
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}
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#else /* #ifdef CONFIG_PREEMPT */
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/*
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* Because preemptible RCU does not exist, we never have to check for
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* tasks blocked within RCU read-side critical sections.
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*/
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static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
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{
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}
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/*
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* Because preemptible RCU does not exist, we never have to check for
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* tasks blocked within RCU read-side critical sections.
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*/
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static int rcu_print_task_stall(struct rcu_node *rnp)
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{
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return 0;
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}
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#endif /* #else #ifdef CONFIG_PREEMPT */
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static void record_gp_stall_check_time(void)
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{
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unsigned long j = jiffies;
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unsigned long j1;
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rcu_state.gp_start = j;
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j1 = rcu_jiffies_till_stall_check();
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/* Record ->gp_start before ->jiffies_stall. */
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smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */
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rcu_state.jiffies_resched = j + j1 / 2;
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rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
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}
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/*
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* Complain about starvation of grace-period kthread.
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*/
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static void rcu_check_gp_kthread_starvation(void)
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{
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struct task_struct *gpk = rcu_state.gp_kthread;
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unsigned long j;
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j = jiffies - READ_ONCE(rcu_state.gp_activity);
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if (j > 2 * HZ) {
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pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
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rcu_state.name, j,
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(long)rcu_seq_current(&rcu_state.gp_seq),
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READ_ONCE(rcu_state.gp_flags),
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gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
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gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
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if (gpk) {
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pr_err("RCU grace-period kthread stack dump:\n");
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sched_show_task(gpk);
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wake_up_process(gpk);
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}
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}
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}
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/*
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* Dump stacks of all tasks running on stalled CPUs. First try using
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* NMIs, but fall back to manual remote stack tracing on architectures
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* that don't support NMI-based stack dumps. The NMI-triggered stack
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* traces are more accurate because they are printed by the target CPU.
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*/
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static void rcu_dump_cpu_stacks(void)
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{
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int cpu;
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unsigned long flags;
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struct rcu_node *rnp;
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rcu_for_each_leaf_node(rnp) {
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raw_spin_lock_irqsave_rcu_node(rnp, flags);
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for_each_leaf_node_possible_cpu(rnp, cpu)
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if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
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if (!trigger_single_cpu_backtrace(cpu))
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dump_cpu_task(cpu);
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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}
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}
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/*
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* If too much time has passed in the current grace period, and if
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* so configured, go kick the relevant kthreads.
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*/
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static void rcu_stall_kick_kthreads(void)
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{
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unsigned long j;
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if (!rcu_kick_kthreads)
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return;
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j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
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if (time_after(jiffies, j) && rcu_state.gp_kthread &&
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(rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
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WARN_ONCE(1, "Kicking %s grace-period kthread\n",
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rcu_state.name);
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rcu_ftrace_dump(DUMP_ALL);
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wake_up_process(rcu_state.gp_kthread);
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WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
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}
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}
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static void panic_on_rcu_stall(void)
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{
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if (sysctl_panic_on_rcu_stall)
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panic("RCU Stall\n");
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}
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static void print_other_cpu_stall(unsigned long gp_seq)
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{
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int cpu;
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unsigned long flags;
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unsigned long gpa;
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unsigned long j;
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int ndetected = 0;
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struct rcu_node *rnp;
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long totqlen = 0;
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/* Kick and suppress, if so configured. */
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rcu_stall_kick_kthreads();
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if (rcu_cpu_stall_suppress)
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return;
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/*
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* OK, time to rat on our buddy...
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* See Documentation/RCU/stallwarn.txt for info on how to debug
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* RCU CPU stall warnings.
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*/
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pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);
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rcu_for_each_leaf_node(rnp) {
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raw_spin_lock_irqsave_rcu_node(rnp, flags);
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ndetected += rcu_print_task_stall(rnp);
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if (rnp->qsmask != 0) {
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for_each_leaf_node_possible_cpu(rnp, cpu)
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if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
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print_cpu_stall_info(cpu);
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ndetected++;
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}
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}
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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}
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for_each_possible_cpu(cpu)
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totqlen += rcu_get_n_cbs_cpu(cpu);
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pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
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smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
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(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
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if (ndetected) {
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rcu_dump_cpu_stacks();
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/* Complain about tasks blocking the grace period. */
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rcu_for_each_leaf_node(rnp)
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rcu_print_detail_task_stall_rnp(rnp);
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} else {
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if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
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pr_err("INFO: Stall ended before state dump start\n");
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} else {
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j = jiffies;
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gpa = READ_ONCE(rcu_state.gp_activity);
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pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
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rcu_state.name, j - gpa, j, gpa,
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READ_ONCE(jiffies_till_next_fqs),
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rcu_get_root()->qsmask);
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/* In this case, the current CPU might be at fault. */
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sched_show_task(current);
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}
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}
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/* Rewrite if needed in case of slow consoles. */
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if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
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WRITE_ONCE(rcu_state.jiffies_stall,
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jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
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rcu_check_gp_kthread_starvation();
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panic_on_rcu_stall();
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rcu_force_quiescent_state(); /* Kick them all. */
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}
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static void print_cpu_stall(void)
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{
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int cpu;
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unsigned long flags;
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struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
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struct rcu_node *rnp = rcu_get_root();
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long totqlen = 0;
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/* Kick and suppress, if so configured. */
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rcu_stall_kick_kthreads();
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if (rcu_cpu_stall_suppress)
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return;
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/*
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* OK, time to rat on ourselves...
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* See Documentation/RCU/stallwarn.txt for info on how to debug
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* RCU CPU stall warnings.
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*/
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pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
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raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
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print_cpu_stall_info(smp_processor_id());
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raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
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for_each_possible_cpu(cpu)
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totqlen += rcu_get_n_cbs_cpu(cpu);
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pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
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jiffies - rcu_state.gp_start,
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(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
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rcu_check_gp_kthread_starvation();
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rcu_dump_cpu_stacks();
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raw_spin_lock_irqsave_rcu_node(rnp, flags);
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/* Rewrite if needed in case of slow consoles. */
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if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
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WRITE_ONCE(rcu_state.jiffies_stall,
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jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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panic_on_rcu_stall();
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/*
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* Attempt to revive the RCU machinery by forcing a context switch.
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*
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* A context switch would normally allow the RCU state machine to make
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* progress and it could be we're stuck in kernel space without context
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* switches for an entirely unreasonable amount of time.
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*/
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set_tsk_need_resched(current);
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set_preempt_need_resched();
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}
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static void check_cpu_stall(struct rcu_data *rdp)
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{
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unsigned long gs1;
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unsigned long gs2;
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unsigned long gps;
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unsigned long j;
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unsigned long jn;
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unsigned long js;
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struct rcu_node *rnp;
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if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
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!rcu_gp_in_progress())
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return;
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rcu_stall_kick_kthreads();
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j = jiffies;
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/*
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* Lots of memory barriers to reject false positives.
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*
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* The idea is to pick up rcu_state.gp_seq, then
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* rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
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* another copy of rcu_state.gp_seq. These values are updated in
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* the opposite order with memory barriers (or equivalent) during
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* grace-period initialization and cleanup. Now, a false positive
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* can occur if we get an new value of rcu_state.gp_start and a old
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* value of rcu_state.jiffies_stall. But given the memory barriers,
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* the only way that this can happen is if one grace period ends
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* and another starts between these two fetches. This is detected
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* by comparing the second fetch of rcu_state.gp_seq with the
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* previous fetch from rcu_state.gp_seq.
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*
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* Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
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* and rcu_state.gp_start suffice to forestall false positives.
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*/
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gs1 = READ_ONCE(rcu_state.gp_seq);
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smp_rmb(); /* Pick up ->gp_seq first... */
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js = READ_ONCE(rcu_state.jiffies_stall);
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smp_rmb(); /* ...then ->jiffies_stall before the rest... */
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gps = READ_ONCE(rcu_state.gp_start);
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smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
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gs2 = READ_ONCE(rcu_state.gp_seq);
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if (gs1 != gs2 ||
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ULONG_CMP_LT(j, js) ||
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ULONG_CMP_GE(gps, js))
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return; /* No stall or GP completed since entering function. */
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rnp = rdp->mynode;
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jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
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if (rcu_gp_in_progress() &&
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(READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
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cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
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/* We haven't checked in, so go dump stack. */
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print_cpu_stall();
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} else if (rcu_gp_in_progress() &&
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ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
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cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
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/* They had a few time units to dump stack, so complain. */
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print_other_cpu_stall(gs2);
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}
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}
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/**
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* rcu_cpu_stall_reset - prevent further stall warnings in current grace period
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*
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* Set the stall-warning timeout way off into the future, thus preventing
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* any RCU CPU stall-warning messages from appearing in the current set of
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* RCU grace periods.
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*
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* The caller must disable hard irqs.
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*/
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void rcu_cpu_stall_reset(void)
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{
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WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
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}
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