// 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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#include <linux/kvm_para.h>
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//////////////////////////////////////////////////////////////////////////////
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//
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// Controlling CPU stall warnings, including delay calculation.
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/* panic() on RCU Stall sysctl. */
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int sysctl_panic_on_rcu_stall __read_mostly = CONFIG_BOOTPARAM_RCU_STALL_PANIC_VALUE;
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ATOMIC_NOTIFIER_HEAD(rcu_stall_notifier_list);
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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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#define RCU_STALL_MIGHT_DIV 8
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#define RCU_STALL_MIGHT_MIN (2 * HZ)
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/* Limit-check stall timeouts specified at boottime and runtime. */
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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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/**
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* rcu_gp_might_be_stalled - Is it likely that the grace period is stalled?
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*
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* Returns @true if the current grace period is sufficiently old that
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* it is reasonable to assume that it might be stalled. This can be
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* useful when deciding whether to allocate memory to enable RCU-mediated
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* freeing on the one hand or just invoking synchronize_rcu() on the other.
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* The latter is preferable when the grace period is stalled.
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*
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* Note that sampling of the .gp_start and .gp_seq fields must be done
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* carefully to avoid false positives at the beginnings and ends of
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* grace periods.
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*/
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bool rcu_gp_might_be_stalled(void)
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{
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unsigned long d = rcu_jiffies_till_stall_check() / RCU_STALL_MIGHT_DIV;
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unsigned long j = jiffies;
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if (d < RCU_STALL_MIGHT_MIN)
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d = RCU_STALL_MIGHT_MIN;
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smp_mb(); // jiffies before .gp_seq to avoid false positives.
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if (!rcu_gp_in_progress())
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return false;
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// Long delays at this point avoids false positive, but a delay
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// of ULONG_MAX/4 jiffies voids your no-false-positive warranty.
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smp_mb(); // .gp_seq before second .gp_start
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// And ditto here.
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return !time_before(j, READ_ONCE(rcu_state.gp_start) + d);
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}
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/* Don't do RCU CPU stall warnings during long sysrq printouts. */
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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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/* Don't print RCU CPU stall warnings during a kernel panic. */
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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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/* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
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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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/**
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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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//////////////////////////////////////////////////////////////////////////////
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//
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// Interaction with RCU grace periods
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/* Start of new grace period, so record stall time (and forcing times). */
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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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WRITE_ONCE(rcu_state.gp_start, j);
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j1 = rcu_jiffies_till_stall_check();
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smp_mb(); // ->gp_start before ->jiffies_stall and caller's ->gp_seq.
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WRITE_ONCE(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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/* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
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static void zero_cpu_stall_ticks(struct rcu_data *rdp)
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{
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rdp->ticks_this_gp = 0;
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rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
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WRITE_ONCE(rdp->last_fqs_resched, jiffies);
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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 (!READ_ONCE(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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/*
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* Handler for the irq_work request posted about halfway into the RCU CPU
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* stall timeout, and used to detect excessive irq disabling. Set state
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* appropriately, but just complain if there is unexpected state on entry.
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*/
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static void rcu_iw_handler(struct irq_work *iwp)
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{
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struct rcu_data *rdp;
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struct rcu_node *rnp;
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rdp = container_of(iwp, struct rcu_data, rcu_iw);
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rnp = rdp->mynode;
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raw_spin_lock_rcu_node(rnp);
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if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
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rdp->rcu_iw_gp_seq = rnp->gp_seq;
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rdp->rcu_iw_pending = false;
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}
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raw_spin_unlock_rcu_node(rnp);
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}
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//////////////////////////////////////////////////////////////////////////////
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//
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// Printing RCU CPU stall warnings
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#ifdef CONFIG_PREEMPT_RCU
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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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// Communicate task state back to the RCU CPU stall warning request.
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struct rcu_stall_chk_rdr {
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int nesting;
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union rcu_special rs;
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bool on_blkd_list;
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};
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/*
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* Report out the state of a not-running task that is stalling the
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* current RCU grace period.
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*/
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static bool check_slow_task(struct task_struct *t, void *arg)
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{
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struct rcu_stall_chk_rdr *rscrp = arg;
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if (task_curr(t))
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return false; // It is running, so decline to inspect it.
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rscrp->nesting = t->rcu_read_lock_nesting;
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rscrp->rs = t->rcu_read_unlock_special;
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rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry);
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return true;
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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 of the first few of them.
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*/
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static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
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__releases(rnp->lock)
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{
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int i = 0;
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int ndetected = 0;
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struct rcu_stall_chk_rdr rscr;
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struct task_struct *t;
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struct task_struct *ts[8];
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lockdep_assert_irqs_disabled();
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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 0;
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}
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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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get_task_struct(t);
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ts[i++] = t;
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if (i >= ARRAY_SIZE(ts))
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break;
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}
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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while (i) {
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t = ts[--i];
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if (!try_invoke_on_locked_down_task(t, check_slow_task, &rscr))
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pr_cont(" P%d", t->pid);
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else
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pr_cont(" P%d/%d:%c%c%c%c",
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t->pid, rscr.nesting,
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".b"[rscr.rs.b.blocked],
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".q"[rscr.rs.b.need_qs],
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".e"[rscr.rs.b.exp_hint],
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".l"[rscr.on_blkd_list]);
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lockdep_assert_irqs_disabled();
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put_task_struct(t);
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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_RCU */
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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, unsigned long flags)
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{
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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return 0;
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}
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#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
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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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#ifdef CONFIG_RCU_FAST_NO_HZ
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static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
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{
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struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
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sprintf(cp, "last_accelerate: %04lx/%04lx dyntick_enabled: %d",
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rdp->last_accelerate & 0xffff, jiffies & 0xffff,
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!!rdp->tick_nohz_enabled_snap);
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}
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#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
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static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
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{
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*cp = '\0';
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}
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#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
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static const char * const gp_state_names[] = {
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[RCU_GP_IDLE] = "RCU_GP_IDLE",
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[RCU_GP_WAIT_GPS] = "RCU_GP_WAIT_GPS",
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[RCU_GP_DONE_GPS] = "RCU_GP_DONE_GPS",
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[RCU_GP_ONOFF] = "RCU_GP_ONOFF",
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[RCU_GP_INIT] = "RCU_GP_INIT",
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[RCU_GP_WAIT_FQS] = "RCU_GP_WAIT_FQS",
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[RCU_GP_DOING_FQS] = "RCU_GP_DOING_FQS",
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[RCU_GP_CLEANUP] = "RCU_GP_CLEANUP",
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[RCU_GP_CLEANED] = "RCU_GP_CLEANED",
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};
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/*
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* Convert a ->gp_state value to a character string.
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*/
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static const char *gp_state_getname(short gs)
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{
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if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
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return "???";
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return gp_state_names[gs];
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}
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/* Is the RCU grace-period kthread being starved of CPU time? */
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static bool rcu_is_gp_kthread_starving(unsigned long *jp)
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{
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unsigned long j = jiffies - READ_ONCE(rcu_state.gp_activity);
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if (jp)
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*jp = j;
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return j > 2 * HZ;
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}
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/*
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* Print out diagnostic information for the specified stalled CPU.
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*
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* If the specified CPU is aware of the current RCU grace period, then
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* print the number of scheduling clock interrupts the CPU has taken
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* during the time that it has been aware. Otherwise, print the number
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* of RCU grace periods that this CPU is ignorant of, for example, "1"
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* if the CPU was aware of the previous grace period.
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*
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* Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
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*/
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static void print_cpu_stall_info(int cpu)
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{
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unsigned long delta;
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bool falsepositive;
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char fast_no_hz[72];
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struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
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char *ticks_title;
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unsigned long ticks_value;
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/*
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* We could be printing a lot while holding a spinlock. Avoid
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* triggering hard lockup.
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*/
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touch_nmi_watchdog();
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ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
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if (ticks_value) {
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ticks_title = "GPs behind";
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} else {
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ticks_title = "ticks this GP";
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ticks_value = rdp->ticks_this_gp;
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}
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print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
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delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
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falsepositive = rcu_is_gp_kthread_starving(NULL) &&
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rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp));
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pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s%s\n",
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cpu,
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"O."[!!cpu_online(cpu)],
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"o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
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"N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
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!IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
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rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
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"!."[!delta],
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ticks_value, ticks_title,
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rcu_dynticks_snap(rdp) & 0xfff,
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rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
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rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
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data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
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fast_no_hz,
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falsepositive ? " (false positive?)" : "");
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}
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/* Complain about starvation of grace-period kthread. */
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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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if (rcu_is_gp_kthread_starving(&j)) {
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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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data_race(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("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name);
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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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static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
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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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lockdep_assert_irqs_disabled();
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/* Kick and suppress, if so configured. */
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rcu_stall_kick_kthreads();
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if (rcu_stall_is_suppressed())
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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.rst for info on how to debug
|
* RCU CPU stall warnings.
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*/
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trace_rcu_stall_warning(rcu_state.name, TPS("StallDetected"));
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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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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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ndetected += rcu_print_task_stall(rnp, flags); // Releases rnp->lock.
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lockdep_assert_irqs_disabled();
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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 - gps),
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(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
|
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 = data_race(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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data_race(jiffies_till_next_fqs),
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rcu_get_root()->qsmask);
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}
|
}
|
/* Rewrite if needed in case of slow consoles. */
|
if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
|
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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atomic_notifier_call_chain(&rcu_stall_notifier_list, 0, NULL);
|
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panic_on_rcu_stall();
|
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rcu_force_quiescent_state(); /* Kick them all. */
|
}
|
|
static void print_cpu_stall(unsigned long gps)
|
{
|
int cpu;
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unsigned long flags;
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
struct rcu_node *rnp = rcu_get_root();
|
long totqlen = 0;
|
|
lockdep_assert_irqs_disabled();
|
|
/* Kick and suppress, if so configured. */
|
rcu_stall_kick_kthreads();
|
if (rcu_stall_is_suppressed())
|
return;
|
|
/*
|
* OK, time to rat on ourselves...
|
* See Documentation/RCU/stallwarn.rst for info on how to debug
|
* RCU CPU stall warnings.
|
*/
|
trace_rcu_stall_warning(rcu_state.name, TPS("SelfDetected"));
|
pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
|
raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
|
print_cpu_stall_info(smp_processor_id());
|
raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
|
for_each_possible_cpu(cpu)
|
totqlen += rcu_get_n_cbs_cpu(cpu);
|
pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
|
jiffies - gps,
|
(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
|
|
rcu_check_gp_kthread_starvation();
|
|
rcu_dump_cpu_stacks();
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
/* Rewrite if needed in case of slow consoles. */
|
if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
|
WRITE_ONCE(rcu_state.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.
|
*/
|
set_tsk_need_resched(current);
|
set_preempt_need_resched();
|
}
|
|
static void check_cpu_stall(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;
|
|
lockdep_assert_irqs_disabled();
|
if ((rcu_stall_is_suppressed() && !READ_ONCE(rcu_kick_kthreads)) ||
|
!rcu_gp_in_progress())
|
return;
|
rcu_stall_kick_kthreads();
|
j = jiffies;
|
|
/*
|
* Lots of memory barriers to reject false positives.
|
*
|
* The idea is to pick up rcu_state.gp_seq, then
|
* rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
|
* another copy of rcu_state.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 rcu_state.gp_start and a old
|
* value of rcu_state.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 rcu_state.gp_seq with the
|
* previous fetch from rcu_state.gp_seq.
|
*
|
* Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
|
* and rcu_state.gp_start suffice to forestall false positives.
|
*/
|
gs1 = READ_ONCE(rcu_state.gp_seq);
|
smp_rmb(); /* Pick up ->gp_seq first... */
|
js = READ_ONCE(rcu_state.jiffies_stall);
|
smp_rmb(); /* ...then ->jiffies_stall before the rest... */
|
gps = READ_ONCE(rcu_state.gp_start);
|
smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
|
gs2 = READ_ONCE(rcu_state.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() &&
|
(READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
|
cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
|
|
/*
|
* If a virtual machine is stopped by the host it can look to
|
* the watchdog like an RCU stall. Check to see if the host
|
* stopped the vm.
|
*/
|
if (kvm_check_and_clear_guest_paused())
|
return;
|
|
/* We haven't checked in, so go dump stack. */
|
print_cpu_stall(gps);
|
if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
|
rcu_ftrace_dump(DUMP_ALL);
|
|
} else if (rcu_gp_in_progress() &&
|
ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
|
cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
|
|
/*
|
* If a virtual machine is stopped by the host it can look to
|
* the watchdog like an RCU stall. Check to see if the host
|
* stopped the vm.
|
*/
|
if (kvm_check_and_clear_guest_paused())
|
return;
|
|
/* They had a few time units to dump stack, so complain. */
|
print_other_cpu_stall(gs2, gps);
|
if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
|
rcu_ftrace_dump(DUMP_ALL);
|
}
|
}
|
|
//////////////////////////////////////////////////////////////////////////////
|
//
|
// RCU forward-progress mechanisms, including of callback invocation.
|
|
|
/*
|
* Show the state of the grace-period kthreads.
|
*/
|
void show_rcu_gp_kthreads(void)
|
{
|
unsigned long cbs = 0;
|
int cpu;
|
unsigned long j;
|
unsigned long ja;
|
unsigned long jr;
|
unsigned long jw;
|
struct rcu_data *rdp;
|
struct rcu_node *rnp;
|
struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
|
|
j = jiffies;
|
ja = j - data_race(rcu_state.gp_activity);
|
jr = j - data_race(rcu_state.gp_req_activity);
|
jw = j - data_race(rcu_state.gp_wake_time);
|
pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
|
rcu_state.name, gp_state_getname(rcu_state.gp_state),
|
rcu_state.gp_state, t ? t->state : 0x1ffffL,
|
ja, jr, jw, (long)data_race(rcu_state.gp_wake_seq),
|
(long)data_race(rcu_state.gp_seq),
|
(long)data_race(rcu_get_root()->gp_seq_needed),
|
data_race(rcu_state.gp_flags));
|
rcu_for_each_node_breadth_first(rnp) {
|
if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),
|
READ_ONCE(rnp->gp_seq_needed)))
|
continue;
|
pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",
|
rnp->grplo, rnp->grphi, (long)data_race(rnp->gp_seq),
|
(long)data_race(rnp->gp_seq_needed));
|
if (!rcu_is_leaf_node(rnp))
|
continue;
|
for_each_leaf_node_possible_cpu(rnp, cpu) {
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
if (READ_ONCE(rdp->gpwrap) ||
|
ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),
|
READ_ONCE(rdp->gp_seq_needed)))
|
continue;
|
pr_info("\tcpu %d ->gp_seq_needed %ld\n",
|
cpu, (long)data_race(rdp->gp_seq_needed));
|
}
|
}
|
for_each_possible_cpu(cpu) {
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
cbs += data_race(rdp->n_cbs_invoked);
|
if (rcu_segcblist_is_offloaded(&rdp->cblist))
|
show_rcu_nocb_state(rdp);
|
}
|
pr_info("RCU callbacks invoked since boot: %lu\n", cbs);
|
show_rcu_tasks_gp_kthreads();
|
}
|
EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
|
|
/*
|
* 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_node *rnp, struct rcu_data *rdp,
|
const unsigned long gpssdelay)
|
{
|
unsigned long flags;
|
unsigned long j;
|
struct rcu_node *rnp_root = rcu_get_root();
|
static atomic_t warned = ATOMIC_INIT(0);
|
|
if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
|
ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
|
READ_ONCE(rnp_root->gp_seq_needed)) ||
|
!smp_load_acquire(&rcu_state.gp_kthread)) // Get stable kthread.
|
return;
|
j = jiffies; /* Expensive access, and in common case don't get here. */
|
if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
|
time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
|
atomic_read(&warned))
|
return;
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
j = jiffies;
|
if (rcu_gp_in_progress() ||
|
ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
|
READ_ONCE(rnp_root->gp_seq_needed)) ||
|
time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
|
time_before(j, READ_ONCE(rcu_state.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() ||
|
ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
|
READ_ONCE(rnp_root->gp_seq_needed)) ||
|
time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
|
time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
|
atomic_xchg(&warned, 1)) {
|
if (rnp_root != rnp)
|
/* irqs remain disabled. */
|
raw_spin_unlock_rcu_node(rnp_root);
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
return;
|
}
|
WARN_ON(1);
|
if (rnp_root != rnp)
|
raw_spin_unlock_rcu_node(rnp_root);
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
show_rcu_gp_kthreads();
|
}
|
|
/*
|
* Do a forward-progress check for rcutorture. This is normally invoked
|
* due to an OOM event. The argument "j" gives the time period during
|
* which rcutorture would like progress to have been made.
|
*/
|
void rcu_fwd_progress_check(unsigned long j)
|
{
|
unsigned long cbs;
|
int cpu;
|
unsigned long max_cbs = 0;
|
int max_cpu = -1;
|
struct rcu_data *rdp;
|
|
if (rcu_gp_in_progress()) {
|
pr_info("%s: GP age %lu jiffies\n",
|
__func__, jiffies - rcu_state.gp_start);
|
show_rcu_gp_kthreads();
|
} else {
|
pr_info("%s: Last GP end %lu jiffies ago\n",
|
__func__, jiffies - rcu_state.gp_end);
|
preempt_disable();
|
rdp = this_cpu_ptr(&rcu_data);
|
rcu_check_gp_start_stall(rdp->mynode, rdp, j);
|
preempt_enable();
|
}
|
for_each_possible_cpu(cpu) {
|
cbs = rcu_get_n_cbs_cpu(cpu);
|
if (!cbs)
|
continue;
|
if (max_cpu < 0)
|
pr_info("%s: callbacks", __func__);
|
pr_cont(" %d: %lu", cpu, cbs);
|
if (cbs <= max_cbs)
|
continue;
|
max_cbs = cbs;
|
max_cpu = cpu;
|
}
|
if (max_cpu >= 0)
|
pr_cont("\n");
|
}
|
EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
|
|
/* Commandeer a sysrq key to dump RCU's tree. */
|
static bool sysrq_rcu;
|
module_param(sysrq_rcu, bool, 0444);
|
|
/* Dump grace-period-request information due to commandeered sysrq. */
|
static void sysrq_show_rcu(int key)
|
{
|
show_rcu_gp_kthreads();
|
}
|
|
static const struct sysrq_key_op sysrq_rcudump_op = {
|
.handler = sysrq_show_rcu,
|
.help_msg = "show-rcu(y)",
|
.action_msg = "Show RCU tree",
|
.enable_mask = SYSRQ_ENABLE_DUMP,
|
};
|
|
static int __init rcu_sysrq_init(void)
|
{
|
if (sysrq_rcu)
|
return register_sysrq_key('y', &sysrq_rcudump_op);
|
return 0;
|
}
|
early_initcall(rcu_sysrq_init);
|
