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993 lines
30 KiB
993 lines
30 KiB
// 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 <[email protected]> |
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*/ |
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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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|
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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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int sysctl_max_rcu_stall_to_panic __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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#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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static int cpu_stall; |
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if (++cpu_stall < sysctl_max_rcu_stall_to_panic) |
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return; |
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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 - restart stall-warning timeout for current grace period |
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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, |
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jiffies + rcu_jiffies_till_stall_check()); |
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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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__releases(rnp->lock) |
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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 (cpu_is_offline(cpu)) |
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pr_err("Offline CPU %d blocking current GP.\n", cpu); |
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else if (!trigger_single_cpu_backtrace(cpu)) |
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dump_cpu_task(cpu); |
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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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#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_ptr(&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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/* |
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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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|
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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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int cpu; |
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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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cpu = gpk ? task_cpu(gpk) : -1; |
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pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x ->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(READ_ONCE(rcu_state.gp_flags)), |
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gp_state_getname(rcu_state.gp_state), |
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data_race(READ_ONCE(rcu_state.gp_state)), |
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gpk ? data_race(READ_ONCE(gpk->__state)) : ~0, cpu); |
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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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if (cpu >= 0) { |
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if (cpu_is_offline(cpu)) { |
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pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); |
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} else { |
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pr_err("Stack dump where RCU GP kthread last ran:\n"); |
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if (!trigger_single_cpu_backtrace(cpu)) |
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dump_cpu_task(cpu); |
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} |
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} |
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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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/* Complain about missing wakeups from expired fqs wait timer */ |
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static void rcu_check_gp_kthread_expired_fqs_timer(void) |
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{ |
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struct task_struct *gpk = rcu_state.gp_kthread; |
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short gp_state; |
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unsigned long jiffies_fqs; |
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int cpu; |
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|
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/* |
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* Order reads of .gp_state and .jiffies_force_qs. |
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* Matching smp_wmb() is present in rcu_gp_fqs_loop(). |
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*/ |
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gp_state = smp_load_acquire(&rcu_state.gp_state); |
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jiffies_fqs = READ_ONCE(rcu_state.jiffies_force_qs); |
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|
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if (gp_state == RCU_GP_WAIT_FQS && |
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time_after(jiffies, jiffies_fqs + RCU_STALL_MIGHT_MIN) && |
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gpk && !READ_ONCE(gpk->on_rq)) { |
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cpu = task_cpu(gpk); |
|
pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x\n", |
|
rcu_state.name, (jiffies - jiffies_fqs), |
|
(long)rcu_seq_current(&rcu_state.gp_seq), |
|
data_race(rcu_state.gp_flags), |
|
gp_state_getname(RCU_GP_WAIT_FQS), RCU_GP_WAIT_FQS, |
|
data_race(READ_ONCE(gpk->__state))); |
|
pr_err("\tPossible timer handling issue on cpu=%d timer-softirq=%u\n", |
|
cpu, kstat_softirqs_cpu(TIMER_SOFTIRQ, cpu)); |
|
} |
|
} |
|
|
|
static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) |
|
{ |
|
int cpu; |
|
unsigned long flags; |
|
unsigned long gpa; |
|
unsigned long j; |
|
int ndetected = 0; |
|
struct rcu_node *rnp; |
|
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 our buddy... |
|
* See Documentation/RCU/stallwarn.rst for info on how to debug |
|
* RCU CPU stall warnings. |
|
*/ |
|
trace_rcu_stall_warning(rcu_state.name, TPS("StallDetected")); |
|
pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name); |
|
rcu_for_each_leaf_node(rnp) { |
|
raw_spin_lock_irqsave_rcu_node(rnp, flags); |
|
if (rnp->qsmask != 0) { |
|
for_each_leaf_node_possible_cpu(rnp, cpu) |
|
if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { |
|
print_cpu_stall_info(cpu); |
|
ndetected++; |
|
} |
|
} |
|
ndetected += rcu_print_task_stall(rnp, flags); // Releases rnp->lock. |
|
lockdep_assert_irqs_disabled(); |
|
} |
|
|
|
for_each_possible_cpu(cpu) |
|
totqlen += rcu_get_n_cbs_cpu(cpu); |
|
pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n", |
|
smp_processor_id(), (long)(jiffies - gps), |
|
(long)rcu_seq_current(&rcu_state.gp_seq), totqlen); |
|
if (ndetected) { |
|
rcu_dump_cpu_stacks(); |
|
|
|
/* Complain about tasks blocking the grace period. */ |
|
rcu_for_each_leaf_node(rnp) |
|
rcu_print_detail_task_stall_rnp(rnp); |
|
} else { |
|
if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) { |
|
pr_err("INFO: Stall ended before state dump start\n"); |
|
} else { |
|
j = jiffies; |
|
gpa = data_race(READ_ONCE(rcu_state.gp_activity)); |
|
pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n", |
|
rcu_state.name, j - gpa, j, gpa, |
|
data_race(READ_ONCE(jiffies_till_next_fqs)), |
|
data_race(READ_ONCE(rcu_get_root()->qsmask))); |
|
} |
|
} |
|
/* 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); |
|
|
|
rcu_check_gp_kthread_expired_fqs_timer(); |
|
rcu_check_gp_kthread_starvation(); |
|
|
|
panic_on_rcu_stall(); |
|
|
|
rcu_force_quiescent_state(); /* Kick them all. */ |
|
} |
|
|
|
static void print_cpu_stall(unsigned long gps) |
|
{ |
|
int cpu; |
|
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_expired_fqs_timer(); |
|
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) |
|
{ |
|
bool didstall = false; |
|
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 + ULONG_MAX / 2; |
|
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); |
|
didstall = true; |
|
|
|
} 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); |
|
didstall = true; |
|
} |
|
if (didstall && READ_ONCE(rcu_state.jiffies_stall) == jn) { |
|
jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3; |
|
WRITE_ONCE(rcu_state.jiffies_stall, jn); |
|
} |
|
} |
|
|
|
////////////////////////////////////////////////////////////////////////////// |
|
// |
|
// RCU forward-progress mechanisms, including of callback invocation. |
|
|
|
|
|
/* |
|
* Check to see if a failure to end RCU priority inversion was due to |
|
* a CPU not passing through a quiescent state. When this happens, there |
|
* is nothing that RCU priority boosting can do to help, so we shouldn't |
|
* count this as an RCU priority boosting failure. A return of true says |
|
* RCU priority boosting is to blame, and false says otherwise. If false |
|
* is returned, the first of the CPUs to blame is stored through cpup. |
|
* If there was no CPU blocking the current grace period, but also nothing |
|
* in need of being boosted, *cpup is set to -1. This can happen in case |
|
* of vCPU preemption while the last CPU is reporting its quiscent state, |
|
* for example. |
|
* |
|
* If cpup is NULL, then a lockless quick check is carried out, suitable |
|
* for high-rate usage. On the other hand, if cpup is non-NULL, each |
|
* rcu_node structure's ->lock is acquired, ruling out high-rate usage. |
|
*/ |
|
bool rcu_check_boost_fail(unsigned long gp_state, int *cpup) |
|
{ |
|
bool atb = false; |
|
int cpu; |
|
unsigned long flags; |
|
struct rcu_node *rnp; |
|
|
|
rcu_for_each_leaf_node(rnp) { |
|
if (!cpup) { |
|
if (data_race(READ_ONCE(rnp->qsmask))) { |
|
return false; |
|
} else { |
|
if (READ_ONCE(rnp->gp_tasks)) |
|
atb = true; |
|
continue; |
|
} |
|
} |
|
*cpup = -1; |
|
raw_spin_lock_irqsave_rcu_node(rnp, flags); |
|
if (rnp->gp_tasks) |
|
atb = true; |
|
if (!rnp->qsmask) { |
|
// No CPUs without quiescent states for this rnp. |
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
|
continue; |
|
} |
|
// Find the first holdout CPU. |
|
for_each_leaf_node_possible_cpu(rnp, cpu) { |
|
if (rnp->qsmask & (1UL << (cpu - rnp->grplo))) { |
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
|
*cpup = cpu; |
|
return false; |
|
} |
|
} |
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
|
} |
|
// Can't blame CPUs, so must blame RCU priority boosting. |
|
return atb; |
|
} |
|
EXPORT_SYMBOL_GPL(rcu_check_boost_fail); |
|
|
|
/* |
|
* 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 js; |
|
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(READ_ONCE(rcu_state.gp_activity)); |
|
jr = j - data_race(READ_ONCE(rcu_state.gp_req_activity)); |
|
js = j - data_race(READ_ONCE(rcu_state.gp_start)); |
|
jw = j - data_race(READ_ONCE(rcu_state.gp_wake_time)); |
|
pr_info("%s: wait state: %s(%d) ->state: %#x ->rt_priority %u delta ->gp_start %lu ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_max %lu ->gp_flags %#x\n", |
|
rcu_state.name, gp_state_getname(rcu_state.gp_state), |
|
data_race(READ_ONCE(rcu_state.gp_state)), |
|
t ? data_race(READ_ONCE(t->__state)) : 0x1ffff, t ? t->rt_priority : 0xffU, |
|
js, ja, jr, jw, (long)data_race(READ_ONCE(rcu_state.gp_wake_seq)), |
|
(long)data_race(READ_ONCE(rcu_state.gp_seq)), |
|
(long)data_race(READ_ONCE(rcu_get_root()->gp_seq_needed)), |
|
data_race(READ_ONCE(rcu_state.gp_max)), |
|
data_race(READ_ONCE(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)) && |
|
!data_race(READ_ONCE(rnp->qsmask)) && !data_race(READ_ONCE(rnp->boost_tasks)) && |
|
!data_race(READ_ONCE(rnp->exp_tasks)) && !data_race(READ_ONCE(rnp->gp_tasks))) |
|
continue; |
|
pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld ->qsmask %#lx %c%c%c%c ->n_boosts %ld\n", |
|
rnp->grplo, rnp->grphi, |
|
(long)data_race(READ_ONCE(rnp->gp_seq)), |
|
(long)data_race(READ_ONCE(rnp->gp_seq_needed)), |
|
data_race(READ_ONCE(rnp->qsmask)), |
|
".b"[!!data_race(READ_ONCE(rnp->boost_kthread_task))], |
|
".B"[!!data_race(READ_ONCE(rnp->boost_tasks))], |
|
".E"[!!data_race(READ_ONCE(rnp->exp_tasks))], |
|
".G"[!!data_race(READ_ONCE(rnp->gp_tasks))], |
|
data_race(READ_ONCE(rnp->n_boosts))); |
|
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(READ_ONCE(rdp->gp_seq_needed))); |
|
} |
|
} |
|
for_each_possible_cpu(cpu) { |
|
rdp = per_cpu_ptr(&rcu_data, cpu); |
|
cbs += data_race(READ_ONCE(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 - data_race(READ_ONCE(rcu_state.gp_start))); |
|
show_rcu_gp_kthreads(); |
|
} else { |
|
pr_info("%s: Last GP end %lu jiffies ago\n", |
|
__func__, jiffies - data_race(READ_ONCE(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); |
|
|
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/* Commandeer a sysrq key to dump RCU's tree. */ |
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static bool sysrq_rcu; |
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module_param(sysrq_rcu, bool, 0444); |
|
|
|
/* Dump grace-period-request information due to commandeered sysrq. */ |
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static void sysrq_show_rcu(int key) |
|
{ |
|
show_rcu_gp_kthreads(); |
|
} |
|
|
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static const struct sysrq_key_op sysrq_rcudump_op = { |
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.handler = sysrq_show_rcu, |
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.help_msg = "show-rcu(y)", |
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.action_msg = "Show RCU tree", |
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.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; |
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} |
|
early_initcall(rcu_sysrq_init);
|
|
|