diff options
Diffstat (limited to 'arch/powerpc/kernel/watchdog.c')
| -rw-r--r-- | arch/powerpc/kernel/watchdog.c | 262 |
1 files changed, 211 insertions, 51 deletions
diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c index af3c15a1d41e..dbcc4a793f0b 100644 --- a/arch/powerpc/kernel/watchdog.c +++ b/arch/powerpc/kernel/watchdog.c @@ -24,9 +24,12 @@ #include <linux/kdebug.h> #include <linux/sched/debug.h> #include <linux/delay.h> +#include <linux/processor.h> #include <linux/smp.h> +#include <asm/interrupt.h> #include <asm/paca.h> +#include <asm/nmi.h> /* * The powerpc watchdog ensures that each CPU is able to service timers. @@ -53,7 +56,7 @@ * solved by also having a SMP watchdog where all CPUs check all other * CPUs heartbeat. * - * The SMP checker can detect lockups on other CPUs. A gobal "pending" + * The SMP checker can detect lockups on other CPUs. A global "pending" * cpumask is kept, containing all CPUs which enable the watchdog. Each * CPU clears their pending bit in their heartbeat timer. When the bitmask * becomes empty, the last CPU to clear its pending bit updates a global @@ -82,10 +85,41 @@ static DEFINE_PER_CPU(u64, wd_timer_tb); /* SMP checker bits */ static unsigned long __wd_smp_lock; +static unsigned long __wd_reporting; +static unsigned long __wd_nmi_output; static cpumask_t wd_smp_cpus_pending; static cpumask_t wd_smp_cpus_stuck; static u64 wd_smp_last_reset_tb; +#ifdef CONFIG_PPC_PSERIES +static u64 wd_timeout_pct; +#endif + +/* + * Try to take the exclusive watchdog action / NMI IPI / printing lock. + * wd_smp_lock must be held. If this fails, we should return and wait + * for the watchdog to kick in again (or another CPU to trigger it). + * + * Importantly, if hardlockup_panic is set, wd_try_report failure should + * not delay the panic, because whichever other CPU is reporting will + * call panic. + */ +static bool wd_try_report(void) +{ + if (__wd_reporting) + return false; + __wd_reporting = 1; + return true; +} + +/* End printing after successful wd_try_report. wd_smp_lock not required. */ +static void wd_end_reporting(void) +{ + smp_mb(); /* End printing "critical section" */ + WARN_ON_ONCE(__wd_reporting == 0); + WRITE_ONCE(__wd_reporting, 0); +} + static inline void wd_smp_lock(unsigned long *flags) { /* @@ -125,108 +159,182 @@ static void wd_lockup_ipi(struct pt_regs *regs) else dump_stack(); + /* + * __wd_nmi_output must be set after we printk from NMI context. + * + * printk from NMI context defers printing to the console to irq_work. + * If that NMI was taken in some code that is hard-locked, then irqs + * are disabled so irq_work will never fire. That can result in the + * hard lockup messages being delayed (indefinitely, until something + * else kicks the console drivers). + * + * Setting __wd_nmi_output will cause another CPU to notice and kick + * the console drivers for us. + * + * xchg is not needed here (it could be a smp_mb and store), but xchg + * gives the memory ordering and atomicity required. + */ + xchg(&__wd_nmi_output, 1); + /* Do not panic from here because that can recurse into NMI IPI layer */ } -static void set_cpumask_stuck(const struct cpumask *cpumask, u64 tb) +static bool set_cpu_stuck(int cpu) { - cpumask_or(&wd_smp_cpus_stuck, &wd_smp_cpus_stuck, cpumask); - cpumask_andnot(&wd_smp_cpus_pending, &wd_smp_cpus_pending, cpumask); + cpumask_set_cpu(cpu, &wd_smp_cpus_stuck); + cpumask_clear_cpu(cpu, &wd_smp_cpus_pending); + /* + * See wd_smp_clear_cpu_pending() + */ + smp_mb(); if (cpumask_empty(&wd_smp_cpus_pending)) { - wd_smp_last_reset_tb = tb; + wd_smp_last_reset_tb = get_tb(); cpumask_andnot(&wd_smp_cpus_pending, &wd_cpus_enabled, &wd_smp_cpus_stuck); + return true; } -} -static void set_cpu_stuck(int cpu, u64 tb) -{ - set_cpumask_stuck(cpumask_of(cpu), tb); + return false; } -static void watchdog_smp_panic(int cpu, u64 tb) +static void watchdog_smp_panic(int cpu) { + static cpumask_t wd_smp_cpus_ipi; // protected by reporting unsigned long flags; + u64 tb, last_reset; int c; wd_smp_lock(&flags); /* Double check some things under lock */ - if ((s64)(tb - wd_smp_last_reset_tb) < (s64)wd_smp_panic_timeout_tb) + tb = get_tb(); + last_reset = wd_smp_last_reset_tb; + if ((s64)(tb - last_reset) < (s64)wd_smp_panic_timeout_tb) goto out; if (cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) goto out; - if (cpumask_weight(&wd_smp_cpus_pending) == 0) + if (!wd_try_report()) + goto out; + for_each_online_cpu(c) { + if (!cpumask_test_cpu(c, &wd_smp_cpus_pending)) + continue; + if (c == cpu) + continue; // should not happen + + __cpumask_set_cpu(c, &wd_smp_cpus_ipi); + if (set_cpu_stuck(c)) + break; + } + if (cpumask_empty(&wd_smp_cpus_ipi)) { + wd_end_reporting(); goto out; + } + wd_smp_unlock(&flags); pr_emerg("CPU %d detected hard LOCKUP on other CPUs %*pbl\n", - cpu, cpumask_pr_args(&wd_smp_cpus_pending)); + cpu, cpumask_pr_args(&wd_smp_cpus_ipi)); pr_emerg("CPU %d TB:%lld, last SMP heartbeat TB:%lld (%lldms ago)\n", - cpu, tb, wd_smp_last_reset_tb, - tb_to_ns(tb - wd_smp_last_reset_tb) / 1000000); + cpu, tb, last_reset, tb_to_ns(tb - last_reset) / 1000000); if (!sysctl_hardlockup_all_cpu_backtrace) { /* * Try to trigger the stuck CPUs, unless we are going to * get a backtrace on all of them anyway. */ - for_each_cpu(c, &wd_smp_cpus_pending) { - if (c == cpu) - continue; + for_each_cpu(c, &wd_smp_cpus_ipi) { smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000); + __cpumask_clear_cpu(c, &wd_smp_cpus_ipi); } - } - - /* Take the stuck CPUs out of the watch group */ - set_cpumask_stuck(&wd_smp_cpus_pending, tb); - - wd_smp_unlock(&flags); - - printk_safe_flush(); - /* - * printk_safe_flush() seems to require another print - * before anything actually goes out to console. - */ - if (sysctl_hardlockup_all_cpu_backtrace) + } else { trigger_allbutself_cpu_backtrace(); + cpumask_clear(&wd_smp_cpus_ipi); + } if (hardlockup_panic) nmi_panic(NULL, "Hard LOCKUP"); + wd_end_reporting(); + return; out: wd_smp_unlock(&flags); } -static void wd_smp_clear_cpu_pending(int cpu, u64 tb) +static void wd_smp_clear_cpu_pending(int cpu) { if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) { if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) { struct pt_regs *regs = get_irq_regs(); unsigned long flags; - wd_smp_lock(&flags); - pr_emerg("CPU %d became unstuck TB:%lld\n", - cpu, tb); + cpu, get_tb()); print_irqtrace_events(current); if (regs) show_regs(regs); else dump_stack(); + wd_smp_lock(&flags); cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck); wd_smp_unlock(&flags); + } else { + /* + * The last CPU to clear pending should have reset the + * watchdog so we generally should not find it empty + * here if our CPU was clear. However it could happen + * due to a rare race with another CPU taking the + * last CPU out of the mask concurrently. + * + * We can't add a warning for it. But just in case + * there is a problem with the watchdog that is causing + * the mask to not be reset, try to kick it along here. + */ + if (unlikely(cpumask_empty(&wd_smp_cpus_pending))) + goto none_pending; } return; } + + /* + * All other updates to wd_smp_cpus_pending are performed under + * wd_smp_lock. All of them are atomic except the case where the + * mask becomes empty and is reset. This will not happen here because + * cpu was tested to be in the bitmap (above), and a CPU only clears + * its own bit. _Except_ in the case where another CPU has detected a + * hard lockup on our CPU and takes us out of the pending mask. So in + * normal operation there will be no race here, no problem. + * + * In the lockup case, this atomic clear-bit vs a store that refills + * other bits in the accessed word wll not be a problem. The bit clear + * is atomic so it will not cause the store to get lost, and the store + * will never set this bit so it will not overwrite the bit clear. The + * only way for a stuck CPU to return to the pending bitmap is to + * become unstuck itself. + */ cpumask_clear_cpu(cpu, &wd_smp_cpus_pending); + + /* + * Order the store to clear pending with the load(s) to check all + * words in the pending mask to check they are all empty. This orders + * with the same barrier on another CPU. This prevents two CPUs + * clearing the last 2 pending bits, but neither seeing the other's + * store when checking if the mask is empty, and missing an empty + * mask, which ends with a false positive. + */ + smp_mb(); if (cpumask_empty(&wd_smp_cpus_pending)) { unsigned long flags; +none_pending: + /* + * Double check under lock because more than one CPU could see + * a clear mask with the lockless check after clearing their + * pending bits. + */ wd_smp_lock(&flags); if (cpumask_empty(&wd_smp_cpus_pending)) { - wd_smp_last_reset_tb = tb; + wd_smp_last_reset_tb = get_tb(); cpumask_andnot(&wd_smp_cpus_pending, &wd_cpus_enabled, &wd_smp_cpus_stuck); @@ -241,33 +349,60 @@ static void watchdog_timer_interrupt(int cpu) per_cpu(wd_timer_tb, cpu) = tb; - wd_smp_clear_cpu_pending(cpu, tb); + wd_smp_clear_cpu_pending(cpu); if ((s64)(tb - wd_smp_last_reset_tb) >= (s64)wd_smp_panic_timeout_tb) - watchdog_smp_panic(cpu, tb); + watchdog_smp_panic(cpu); + + if (__wd_nmi_output && xchg(&__wd_nmi_output, 0)) { + /* + * Something has called printk from NMI context. It might be + * stuck, so this triggers a flush that will get that + * printk output to the console. + * + * See wd_lockup_ipi. + */ + printk_trigger_flush(); + } } -void soft_nmi_interrupt(struct pt_regs *regs) +DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt) { unsigned long flags; int cpu = raw_smp_processor_id(); u64 tb; - if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) - return; + /* should only arrive from kernel, with irqs disabled */ + WARN_ON_ONCE(!arch_irq_disabled_regs(regs)); - nmi_enter(); + if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) + return 0; __this_cpu_inc(irq_stat.soft_nmi_irqs); tb = get_tb(); if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) { + /* + * Taking wd_smp_lock here means it is a soft-NMI lock, which + * means we can't take any regular or irqsafe spin locks while + * holding this lock. This is why timers can't printk while + * holding the lock. + */ wd_smp_lock(&flags); if (cpumask_test_cpu(cpu, &wd_smp_cpus_stuck)) { wd_smp_unlock(&flags); - goto out; + return 0; + } + if (!wd_try_report()) { + wd_smp_unlock(&flags); + /* Couldn't report, try again in 100ms */ + mtspr(SPRN_DEC, 100 * tb_ticks_per_usec * 1000); + return 0; } - set_cpu_stuck(cpu, tb); + + set_cpu_stuck(cpu); + + wd_smp_unlock(&flags); pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n", cpu, (void *)regs->nip); @@ -278,19 +413,25 @@ void soft_nmi_interrupt(struct pt_regs *regs) print_irqtrace_events(current); show_regs(regs); - wd_smp_unlock(&flags); + xchg(&__wd_nmi_output, 1); // see wd_lockup_ipi if (sysctl_hardlockup_all_cpu_backtrace) trigger_allbutself_cpu_backtrace(); if (hardlockup_panic) nmi_panic(regs, "Hard LOCKUP"); + + wd_end_reporting(); } + /* + * We are okay to change DEC in soft_nmi_interrupt because the masked + * handler has marked a DEC as pending, so the timer interrupt will be + * replayed as soon as local irqs are enabled again. + */ if (wd_panic_timeout_tb < 0x7fffffff) mtspr(SPRN_DEC, wd_panic_timeout_tb); -out: - nmi_exit(); + return 0; } static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) @@ -314,11 +455,15 @@ void arch_touch_nmi_watchdog(void) { unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000; int cpu = smp_processor_id(); - u64 tb = get_tb(); + u64 tb; + if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) + return; + + tb = get_tb(); if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) { per_cpu(wd_timer_tb, cpu) = tb; - wd_smp_clear_cpu_pending(cpu, tb); + wd_smp_clear_cpu_pending(cpu); } } EXPORT_SYMBOL(arch_touch_nmi_watchdog); @@ -376,7 +521,7 @@ static void stop_watchdog(void *arg) cpumask_clear_cpu(cpu, &wd_cpus_enabled); wd_smp_unlock(&flags); - wd_smp_clear_cpu_pending(cpu, get_tb()); + wd_smp_clear_cpu_pending(cpu); } static int stop_watchdog_on_cpu(unsigned int cpu) @@ -386,7 +531,13 @@ static int stop_watchdog_on_cpu(unsigned int cpu) static void watchdog_calc_timeouts(void) { - wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq; + u64 threshold = watchdog_thresh; + +#ifdef CONFIG_PPC_PSERIES + threshold += (READ_ONCE(wd_timeout_pct) * threshold) / 100; +#endif + + wd_panic_timeout_tb = threshold * ppc_tb_freq; /* Have the SMP detector trigger a bit later */ wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2; @@ -429,3 +580,12 @@ int __init watchdog_nmi_probe(void) } return 0; } + +#ifdef CONFIG_PPC_PSERIES +void watchdog_nmi_set_timeout_pct(u64 pct) +{ + pr_info("Set the NMI watchdog timeout factor to %llu%%\n", pct); + WRITE_ONCE(wd_timeout_pct, pct); + lockup_detector_reconfigure(); +} +#endif |