From 896260a6d69d01ceb1aad8cfe4298bd837a67432 Mon Sep 17 00:00:00 2001 From: Douglas Anderson Date: Wed, 20 Dec 2023 13:15:35 -0800 Subject: watchdog/softlockup: use printk_cpu_sync_get_irqsave() to serialize reporting Instead of introducing a spinlock, use printk_cpu_sync_get_irqsave() and printk_cpu_sync_put_irqrestore() to serialize softlockup reporting. Alone this doesn't have any real advantage over the spinlock, but this will allow us to use the same function in a future change to also serialize hardlockup crawls. NOTE: for the most part this serialization is important because we often end up in the show_regs() path and that has no built-in serialization if there are multiple callers at once. However, even in the case where we end up in the dump_stack() path this still has some advantages because the stack will be guaranteed to be together in the logs with the lockup message with no interleaving. NOTE: the fact that printk_cpu_sync_get_irqsave() is allowed to be called multiple times on the same CPU is important here. Specifically we hold the "lock" while calling dump_stack() which also gets the same "lock". This is explicitly documented to be OK and means we don't need to introduce a variant of dump_stack() that doesn't grab the lock. Link: https://lkml.kernel.org/r/20231220131534.2.Ia5906525d440d8e8383cde31b7c61c2aadc8f907@changeid Signed-off-by: Douglas Anderson Reviewed-by: John Ogness Reviewed-by: Li Zhe Cc: Lecopzer Chen Cc: Petr Mladek Cc: Pingfan Liu Signed-off-by: Andrew Morton --- kernel/watchdog.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index b4fd2f12137f..526041a1100a 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -454,7 +454,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) struct pt_regs *regs = get_irq_regs(); int duration; int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace; - static DEFINE_SPINLOCK(watchdog_output_lock); + unsigned long flags; if (!watchdog_enabled) return HRTIMER_NORESTART; @@ -521,7 +521,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) /* Start period for the next softlockup warning. */ update_report_ts(); - spin_lock(&watchdog_output_lock); + printk_cpu_sync_get_irqsave(flags); pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", smp_processor_id(), duration, current->comm, task_pid_nr(current)); @@ -531,7 +531,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) show_regs(regs); else dump_stack(); - spin_unlock(&watchdog_output_lock); + printk_cpu_sync_put_irqrestore(flags); if (softlockup_all_cpu_backtrace) { trigger_allbutcpu_cpu_backtrace(smp_processor_id()); -- cgit