diff options
Diffstat (limited to 'arch/powerpc/kernel/watchdog.c')
| -rw-r--r-- | arch/powerpc/kernel/watchdog.c | 591 |
1 files changed, 591 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c new file mode 100644 index 0000000000..8c464a5d82 --- /dev/null +++ b/arch/powerpc/kernel/watchdog.c @@ -0,0 +1,591 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Watchdog support on powerpc systems. + * + * Copyright 2017, IBM Corporation. + * + * This uses code from arch/sparc/kernel/nmi.c and kernel/watchdog.c + */ + +#define pr_fmt(fmt) "watchdog: " fmt + +#include <linux/kernel.h> +#include <linux/param.h> +#include <linux/init.h> +#include <linux/percpu.h> +#include <linux/cpu.h> +#include <linux/nmi.h> +#include <linux/module.h> +#include <linux/export.h> +#include <linux/kprobes.h> +#include <linux/hardirq.h> +#include <linux/reboot.h> +#include <linux/slab.h> +#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. + * The watchdog sets up a simple timer on each CPU to run once per timer + * period, and updates a per-cpu timestamp and a "pending" cpumask. This is + * the heartbeat. + * + * Then there are two systems to check that the heartbeat is still running. + * The local soft-NMI, and the SMP checker. + * + * The soft-NMI checker can detect lockups on the local CPU. When interrupts + * are disabled with local_irq_disable(), platforms that use soft-masking + * can leave hardware interrupts enabled and handle them with a masked + * interrupt handler. The masked handler can send the timer interrupt to the + * watchdog's soft_nmi_interrupt(), which appears to Linux as an NMI + * interrupt, and can be used to detect CPUs stuck with IRQs disabled. + * + * The soft-NMI checker will compare the heartbeat timestamp for this CPU + * with the current time, and take action if the difference exceeds the + * watchdog threshold. + * + * The limitation of the soft-NMI watchdog is that it does not work when + * interrupts are hard disabled or otherwise not being serviced. This is + * 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 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 + * timestamp and refills the pending bitmask. + * + * In the heartbeat timer, if any CPU notices that the global timestamp has + * not been updated for a period exceeding the watchdog threshold, then it + * means the CPU(s) with their bit still set in the pending mask have had + * their heartbeat stop, and action is taken. + * + * Some platforms implement true NMI IPIs, which can be used by the SMP + * watchdog to detect an unresponsive CPU and pull it out of its stuck + * state with the NMI IPI, to get crash/debug data from it. This way the + * SMP watchdog can detect hardware interrupts off lockups. + */ + +static cpumask_t wd_cpus_enabled __read_mostly; + +static u64 wd_panic_timeout_tb __read_mostly; /* timebase ticks until panic */ +static u64 wd_smp_panic_timeout_tb __read_mostly; /* panic other CPUs */ + +static u64 wd_timer_period_ms __read_mostly; /* interval between heartbeat */ + +static DEFINE_PER_CPU(struct hrtimer, wd_hrtimer); +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) +{ + /* + * Avoid locking layers if possible. + * This may be called from low level interrupt handlers at some + * point in future. + */ + raw_local_irq_save(*flags); + hard_irq_disable(); /* Make it soft-NMI safe */ + while (unlikely(test_and_set_bit_lock(0, &__wd_smp_lock))) { + raw_local_irq_restore(*flags); + spin_until_cond(!test_bit(0, &__wd_smp_lock)); + raw_local_irq_save(*flags); + hard_irq_disable(); + } +} + +static inline void wd_smp_unlock(unsigned long *flags) +{ + clear_bit_unlock(0, &__wd_smp_lock); + raw_local_irq_restore(*flags); +} + +static void wd_lockup_ipi(struct pt_regs *regs) +{ + int cpu = raw_smp_processor_id(); + u64 tb = get_tb(); + + pr_emerg("CPU %d Hard LOCKUP\n", cpu); + pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n", + cpu, tb, per_cpu(wd_timer_tb, cpu), + tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000); + print_modules(); + print_irqtrace_events(current); + if (regs) + show_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 bool set_cpu_stuck(int cpu) +{ + 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 = get_tb(); + cpumask_andnot(&wd_smp_cpus_pending, + &wd_cpus_enabled, + &wd_smp_cpus_stuck); + return true; + } + return false; +} + +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 */ + 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 (!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_ipi)); + pr_emerg("CPU %d TB:%lld, last SMP heartbeat TB:%lld (%lldms ago)\n", + 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_ipi) { + smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000); + __cpumask_clear_cpu(c, &wd_smp_cpus_ipi); + } + } else { + trigger_allbutcpu_cpu_backtrace(cpu); + 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) +{ + 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; + + pr_emerg("CPU %d became unstuck TB:%lld\n", + 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 = get_tb(); + cpumask_andnot(&wd_smp_cpus_pending, + &wd_cpus_enabled, + &wd_smp_cpus_stuck); + } + wd_smp_unlock(&flags); + } +} + +static void watchdog_timer_interrupt(int cpu) +{ + u64 tb = get_tb(); + + per_cpu(wd_timer_tb, 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); + + 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(); + } +} + +DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt) +{ + unsigned long flags; + int cpu = raw_smp_processor_id(); + u64 tb; + + /* should only arrive from kernel, with irqs disabled */ + WARN_ON_ONCE(!arch_irq_disabled_regs(regs)); + + 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); + 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); + + wd_smp_unlock(&flags); + + pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n", + cpu, (void *)regs->nip); + pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n", + cpu, tb, per_cpu(wd_timer_tb, cpu), + tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000); + print_modules(); + print_irqtrace_events(current); + show_regs(regs); + + xchg(&__wd_nmi_output, 1); // see wd_lockup_ipi + + if (sysctl_hardlockup_all_cpu_backtrace) + trigger_allbutcpu_cpu_backtrace(cpu); + + 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); + + return 0; +} + +static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) +{ + int cpu = smp_processor_id(); + + if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED)) + return HRTIMER_NORESTART; + + if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) + return HRTIMER_NORESTART; + + watchdog_timer_interrupt(cpu); + + hrtimer_forward_now(hrtimer, ms_to_ktime(wd_timer_period_ms)); + + return HRTIMER_RESTART; +} + +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; + + 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); + } +} +EXPORT_SYMBOL(arch_touch_nmi_watchdog); + +static void start_watchdog(void *arg) +{ + struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer); + int cpu = smp_processor_id(); + unsigned long flags; + + if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) { + WARN_ON(1); + return; + } + + if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED)) + return; + + if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) + return; + + wd_smp_lock(&flags); + cpumask_set_cpu(cpu, &wd_cpus_enabled); + if (cpumask_weight(&wd_cpus_enabled) == 1) { + cpumask_set_cpu(cpu, &wd_smp_cpus_pending); + wd_smp_last_reset_tb = get_tb(); + } + wd_smp_unlock(&flags); + + *this_cpu_ptr(&wd_timer_tb) = get_tb(); + + hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + hrtimer->function = watchdog_timer_fn; + hrtimer_start(hrtimer, ms_to_ktime(wd_timer_period_ms), + HRTIMER_MODE_REL_PINNED); +} + +static int start_watchdog_on_cpu(unsigned int cpu) +{ + return smp_call_function_single(cpu, start_watchdog, NULL, true); +} + +static void stop_watchdog(void *arg) +{ + struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer); + int cpu = smp_processor_id(); + unsigned long flags; + + if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) + return; /* Can happen in CPU unplug case */ + + hrtimer_cancel(hrtimer); + + wd_smp_lock(&flags); + cpumask_clear_cpu(cpu, &wd_cpus_enabled); + wd_smp_unlock(&flags); + + wd_smp_clear_cpu_pending(cpu); +} + +static int stop_watchdog_on_cpu(unsigned int cpu) +{ + return smp_call_function_single(cpu, stop_watchdog, NULL, true); +} + +static void watchdog_calc_timeouts(void) +{ + 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; + + /* 2/5 is the factor that the perf based detector uses */ + wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5; +} + +void watchdog_hardlockup_stop(void) +{ + int cpu; + + for_each_cpu(cpu, &wd_cpus_enabled) + stop_watchdog_on_cpu(cpu); +} + +void watchdog_hardlockup_start(void) +{ + int cpu; + + watchdog_calc_timeouts(); + for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) + start_watchdog_on_cpu(cpu); +} + +/* + * Invoked from core watchdog init. + */ +int __init watchdog_hardlockup_probe(void) +{ + int err; + + err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, + "powerpc/watchdog:online", + start_watchdog_on_cpu, + stop_watchdog_on_cpu); + if (err < 0) { + pr_warn("could not be initialized"); + return err; + } + return 0; +} + +#ifdef CONFIG_PPC_PSERIES +void watchdog_hardlockup_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 |