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- // SPDX-License-Identifier: GPL-2.0+
- /*
- * RCU CPU stall warnings for normal RCU grace periods
- *
- * Copyright IBM Corporation, 2019
- *
- * Author: Paul E. McKenney <paulmck@linux.ibm.com>
- */
- #include <linux/kvm_para.h>
- //////////////////////////////////////////////////////////////////////////////
- //
- // Controlling CPU stall warnings, including delay calculation.
- /* panic() on RCU Stall sysctl. */
- int sysctl_panic_on_rcu_stall __read_mostly;
- #ifdef CONFIG_PROVE_RCU
- #define RCU_STALL_DELAY_DELTA (5 * HZ)
- #else
- #define RCU_STALL_DELAY_DELTA 0
- #endif
- #define RCU_STALL_MIGHT_DIV 8
- #define RCU_STALL_MIGHT_MIN (2 * HZ)
- /* Limit-check stall timeouts specified at boottime and runtime. */
- int rcu_jiffies_till_stall_check(void)
- {
- int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
- /*
- * Limit check must be consistent with the Kconfig limits
- * for CONFIG_RCU_CPU_STALL_TIMEOUT.
- */
- if (till_stall_check < 3) {
- WRITE_ONCE(rcu_cpu_stall_timeout, 3);
- till_stall_check = 3;
- } else if (till_stall_check > 300) {
- WRITE_ONCE(rcu_cpu_stall_timeout, 300);
- till_stall_check = 300;
- }
- return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
- }
- EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);
- /**
- * rcu_gp_might_be_stalled - Is it likely that the grace period is stalled?
- *
- * Returns @true if the current grace period is sufficiently old that
- * it is reasonable to assume that it might be stalled. This can be
- * useful when deciding whether to allocate memory to enable RCU-mediated
- * freeing on the one hand or just invoking synchronize_rcu() on the other.
- * The latter is preferable when the grace period is stalled.
- *
- * Note that sampling of the .gp_start and .gp_seq fields must be done
- * carefully to avoid false positives at the beginnings and ends of
- * grace periods.
- */
- bool rcu_gp_might_be_stalled(void)
- {
- unsigned long d = rcu_jiffies_till_stall_check() / RCU_STALL_MIGHT_DIV;
- unsigned long j = jiffies;
- if (d < RCU_STALL_MIGHT_MIN)
- d = RCU_STALL_MIGHT_MIN;
- smp_mb(); // jiffies before .gp_seq to avoid false positives.
- if (!rcu_gp_in_progress())
- return false;
- // Long delays at this point avoids false positive, but a delay
- // of ULONG_MAX/4 jiffies voids your no-false-positive warranty.
- smp_mb(); // .gp_seq before second .gp_start
- // And ditto here.
- return !time_before(j, READ_ONCE(rcu_state.gp_start) + d);
- }
- /* Don't do RCU CPU stall warnings during long sysrq printouts. */
- void rcu_sysrq_start(void)
- {
- if (!rcu_cpu_stall_suppress)
- rcu_cpu_stall_suppress = 2;
- }
- void rcu_sysrq_end(void)
- {
- if (rcu_cpu_stall_suppress == 2)
- rcu_cpu_stall_suppress = 0;
- }
- /* Don't print RCU CPU stall warnings during a kernel panic. */
- static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
- {
- rcu_cpu_stall_suppress = 1;
- return NOTIFY_DONE;
- }
- static struct notifier_block rcu_panic_block = {
- .notifier_call = rcu_panic,
- };
- static int __init check_cpu_stall_init(void)
- {
- atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
- return 0;
- }
- early_initcall(check_cpu_stall_init);
- /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
- static void panic_on_rcu_stall(void)
- {
- if (sysctl_panic_on_rcu_stall)
- panic("RCU Stall\n");
- }
- /**
- * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
- *
- * Set the stall-warning timeout way off into the future, thus preventing
- * any RCU CPU stall-warning messages from appearing in the current set of
- * RCU grace periods.
- *
- * The caller must disable hard irqs.
- */
- void rcu_cpu_stall_reset(void)
- {
- WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
- }
- //////////////////////////////////////////////////////////////////////////////
- //
- // Interaction with RCU grace periods
- /* Start of new grace period, so record stall time (and forcing times). */
- static void record_gp_stall_check_time(void)
- {
- unsigned long j = jiffies;
- unsigned long j1;
- WRITE_ONCE(rcu_state.gp_start, j);
- j1 = rcu_jiffies_till_stall_check();
- smp_mb(); // ->gp_start before ->jiffies_stall and caller's ->gp_seq.
- WRITE_ONCE(rcu_state.jiffies_stall, j + j1);
- rcu_state.jiffies_resched = j + j1 / 2;
- rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
- }
- /* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
- static void zero_cpu_stall_ticks(struct rcu_data *rdp)
- {
- rdp->ticks_this_gp = 0;
- rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
- WRITE_ONCE(rdp->last_fqs_resched, jiffies);
- }
- /*
- * If too much time has passed in the current grace period, and if
- * so configured, go kick the relevant kthreads.
- */
- static void rcu_stall_kick_kthreads(void)
- {
- unsigned long j;
- if (!READ_ONCE(rcu_kick_kthreads))
- return;
- j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
- if (time_after(jiffies, j) && rcu_state.gp_kthread &&
- (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
- WARN_ONCE(1, "Kicking %s grace-period kthread\n",
- rcu_state.name);
- rcu_ftrace_dump(DUMP_ALL);
- wake_up_process(rcu_state.gp_kthread);
- WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
- }
- }
- /*
- * Handler for the irq_work request posted about halfway into the RCU CPU
- * stall timeout, and used to detect excessive irq disabling. Set state
- * appropriately, but just complain if there is unexpected state on entry.
- */
- static void rcu_iw_handler(struct irq_work *iwp)
- {
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- rdp = container_of(iwp, struct rcu_data, rcu_iw);
- rnp = rdp->mynode;
- raw_spin_lock_rcu_node(rnp);
- if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
- rdp->rcu_iw_gp_seq = rnp->gp_seq;
- rdp->rcu_iw_pending = false;
- }
- raw_spin_unlock_rcu_node(rnp);
- }
- //////////////////////////////////////////////////////////////////////////////
- //
- // Printing RCU CPU stall warnings
- #ifdef CONFIG_PREEMPT_RCU
- /*
- * Dump detailed information for all tasks blocking the current RCU
- * grace period on the specified rcu_node structure.
- */
- static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
- {
- unsigned long flags;
- struct task_struct *t;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- if (!rcu_preempt_blocked_readers_cgp(rnp)) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return;
- }
- t = list_entry(rnp->gp_tasks->prev,
- struct task_struct, rcu_node_entry);
- list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
- /*
- * We could be printing a lot while holding a spinlock.
- * Avoid triggering hard lockup.
- */
- touch_nmi_watchdog();
- sched_show_task(t);
- }
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- // Communicate task state back to the RCU CPU stall warning request.
- struct rcu_stall_chk_rdr {
- int nesting;
- union rcu_special rs;
- bool on_blkd_list;
- };
- /*
- * Report out the state of a not-running task that is stalling the
- * current RCU grace period.
- */
- static bool check_slow_task(struct task_struct *t, void *arg)
- {
- struct rcu_stall_chk_rdr *rscrp = arg;
- if (task_curr(t))
- return false; // It is running, so decline to inspect it.
- rscrp->nesting = t->rcu_read_lock_nesting;
- rscrp->rs = t->rcu_read_unlock_special;
- rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry);
- return true;
- }
- /*
- * Scan the current list of tasks blocked within RCU read-side critical
- * sections, printing out the tid of each of the first few of them.
- */
- static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
- __releases(rnp->lock)
- {
- int i = 0;
- int ndetected = 0;
- struct rcu_stall_chk_rdr rscr;
- struct task_struct *t;
- struct task_struct *ts[8];
- lockdep_assert_irqs_disabled();
- if (!rcu_preempt_blocked_readers_cgp(rnp)) {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return 0;
- }
- pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
- rnp->level, rnp->grplo, rnp->grphi);
- t = list_entry(rnp->gp_tasks->prev,
- struct task_struct, rcu_node_entry);
- list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
- get_task_struct(t);
- ts[i++] = t;
- if (i >= ARRAY_SIZE(ts))
- break;
- }
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- while (i) {
- t = ts[--i];
- if (!try_invoke_on_locked_down_task(t, check_slow_task, &rscr))
- pr_cont(" P%d", t->pid);
- else
- pr_cont(" P%d/%d:%c%c%c%c",
- t->pid, rscr.nesting,
- ".b"[rscr.rs.b.blocked],
- ".q"[rscr.rs.b.need_qs],
- ".e"[rscr.rs.b.exp_hint],
- ".l"[rscr.on_blkd_list]);
- lockdep_assert_irqs_disabled();
- put_task_struct(t);
- ndetected++;
- }
- pr_cont("\n");
- return ndetected;
- }
- #else /* #ifdef CONFIG_PREEMPT_RCU */
- /*
- * Because preemptible RCU does not exist, we never have to check for
- * tasks blocked within RCU read-side critical sections.
- */
- static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
- {
- }
- /*
- * Because preemptible RCU does not exist, we never have to check for
- * tasks blocked within RCU read-side critical sections.
- */
- static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
- {
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- return 0;
- }
- #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
- /*
- * Dump stacks of all tasks running on stalled CPUs. First try using
- * NMIs, but fall back to manual remote stack tracing on architectures
- * that don't support NMI-based stack dumps. The NMI-triggered stack
- * traces are more accurate because they are printed by the target CPU.
- */
- static void rcu_dump_cpu_stacks(void)
- {
- int cpu;
- unsigned long flags;
- struct rcu_node *rnp;
- rcu_for_each_leaf_node(rnp) {
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- for_each_leaf_node_possible_cpu(rnp, cpu)
- if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
- if (!trigger_single_cpu_backtrace(cpu))
- dump_cpu_task(cpu);
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- }
- }
- #ifdef CONFIG_RCU_FAST_NO_HZ
- static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
- {
- struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
- sprintf(cp, "last_accelerate: %04lx/%04lx dyntick_enabled: %d",
- rdp->last_accelerate & 0xffff, jiffies & 0xffff,
- !!rdp->tick_nohz_enabled_snap);
- }
- #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
- static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
- {
- *cp = '\0';
- }
- #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
- static const char * const gp_state_names[] = {
- [RCU_GP_IDLE] = "RCU_GP_IDLE",
- [RCU_GP_WAIT_GPS] = "RCU_GP_WAIT_GPS",
- [RCU_GP_DONE_GPS] = "RCU_GP_DONE_GPS",
- [RCU_GP_ONOFF] = "RCU_GP_ONOFF",
- [RCU_GP_INIT] = "RCU_GP_INIT",
- [RCU_GP_WAIT_FQS] = "RCU_GP_WAIT_FQS",
- [RCU_GP_DOING_FQS] = "RCU_GP_DOING_FQS",
- [RCU_GP_CLEANUP] = "RCU_GP_CLEANUP",
- [RCU_GP_CLEANED] = "RCU_GP_CLEANED",
- };
- /*
- * Convert a ->gp_state value to a character string.
- */
- static const char *gp_state_getname(short gs)
- {
- if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
- return "???";
- return gp_state_names[gs];
- }
- /* Is the RCU grace-period kthread being starved of CPU time? */
- static bool rcu_is_gp_kthread_starving(unsigned long *jp)
- {
- unsigned long j = jiffies - READ_ONCE(rcu_state.gp_activity);
- if (jp)
- *jp = j;
- return j > 2 * HZ;
- }
- /*
- * Print out diagnostic information for the specified stalled CPU.
- *
- * If the specified CPU is aware of the current RCU grace period, then
- * print the number of scheduling clock interrupts the CPU has taken
- * during the time that it has been aware. Otherwise, print the number
- * of RCU grace periods that this CPU is ignorant of, for example, "1"
- * if the CPU was aware of the previous grace period.
- *
- * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
- */
- static void print_cpu_stall_info(int cpu)
- {
- unsigned long delta;
- bool falsepositive;
- char fast_no_hz[72];
- struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
- char *ticks_title;
- unsigned long ticks_value;
- /*
- * We could be printing a lot while holding a spinlock. Avoid
- * triggering hard lockup.
- */
- touch_nmi_watchdog();
- ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
- if (ticks_value) {
- ticks_title = "GPs behind";
- } else {
- ticks_title = "ticks this GP";
- ticks_value = rdp->ticks_this_gp;
- }
- print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
- delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
- falsepositive = rcu_is_gp_kthread_starving(NULL) &&
- rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp));
- pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s%s\n",
- cpu,
- "O."[!!cpu_online(cpu)],
- "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
- "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
- !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
- rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
- "!."[!delta],
- ticks_value, ticks_title,
- rcu_dynticks_snap(rdp) & 0xfff,
- rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
- rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
- data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
- fast_no_hz,
- falsepositive ? " (false positive?)" : "");
- }
- /* Complain about starvation of grace-period kthread. */
- static void rcu_check_gp_kthread_starvation(void)
- {
- struct task_struct *gpk = rcu_state.gp_kthread;
- unsigned long j;
- if (rcu_is_gp_kthread_starving(&j)) {
- pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
- rcu_state.name, j,
- (long)rcu_seq_current(&rcu_state.gp_seq),
- data_race(rcu_state.gp_flags),
- gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
- gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
- if (gpk) {
- pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name);
- pr_err("RCU grace-period kthread stack dump:\n");
- sched_show_task(gpk);
- wake_up_process(gpk);
- }
- }
- }
- 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(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(jiffies_till_next_fqs),
- 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_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_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);
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