Softlockup report means that there is no progress on the given CPU. It might be a "short" affair where the system gets recovered. But often the system stops being responsive and need to get rebooted.
The softlockup might be root of the problems or just a symptom. It might be a deadlock, livelock, or often repeated state. Regular reports help to distinguish different situations. Fortunately, the watchdog is finally able to show correct information how long softlockup_fn() was not scheduled. Note that the horrible code never really worked before the accounting was fixed. The last working timestamp was regularly lost by the many touch*watchdog() calls. Also note that the full report is useful to distinguish livelock and deadlock. Signed-off-by: Petr Mladek <[email protected]> --- kernel/watchdog.c | 25 +------------------------ 1 file changed, 1 insertion(+), 24 deletions(-) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index bd249676ee3d..2058229ed398 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -173,10 +173,8 @@ static DEFINE_PER_CPU(unsigned long, watchdog_period_ts); static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer); static DEFINE_PER_CPU(bool, watchdog_restart_period); static DEFINE_PER_CPU(bool, softlockup_touch_sync); -static DEFINE_PER_CPU(bool, soft_watchdog_warn); static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts); static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt); -static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved); static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved); static unsigned long soft_lockup_nmi_warn; @@ -268,7 +266,6 @@ static void __touch_watchdog(void) { __this_cpu_write(watchdog_touch_ts, get_timestamp()); __restart_watchdog_period(); - __this_cpu_write(soft_watchdog_warn, false); } /** @@ -429,31 +426,13 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) if (kvm_check_and_clear_guest_paused()) return HRTIMER_RESTART; - /* only warn once */ - if (__this_cpu_read(soft_watchdog_warn) == true) { - /* - * When multiple processes are causing softlockups the - * softlockup detector only warns on the first one - * because the code relies on a full quiet cycle to - * re-arm. The second process prevents the quiet cycle - * and never gets reported. Use task pointers to detect - * this. - */ - if (__this_cpu_read(softlockup_task_ptr_saved) != - current) { - __this_cpu_write(soft_watchdog_warn, false); - __restart_watchdog_period(); - } - return HRTIMER_RESTART; - } - if (softlockup_all_cpu_backtrace) { /* Prevent multiple soft-lockup reports if one cpu is already * engaged in dumping cpu back traces */ if (test_and_set_bit(0, &soft_lockup_nmi_warn)) { /* Someone else will report us. Let's give up */ - __this_cpu_write(soft_watchdog_warn, true); + __restart_watchdog_period(); return HRTIMER_RESTART; } } @@ -461,7 +440,6 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", smp_processor_id(), duration, current->comm, task_pid_nr(current)); - __this_cpu_write(softlockup_task_ptr_saved, current); print_modules(); print_irqtrace_events(current); if (regs) @@ -483,7 +461,6 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK); if (softlockup_panic) panic("softlockup: hung tasks"); - __this_cpu_write(soft_watchdog_warn, true); } return HRTIMER_RESTART; -- 2.16.4
