| // 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 |