For now, soft lockup detector warns once for each case of process softlockup. But the thread 'watchdog/n' may not always get the cpu at the time slot between the task switch of two processes hogging that cpu to reset soft_watchdog_warn.
An example would be two processes hogging the cpu. Process A causes the softlockup warning and is killed manually by a user. Process B immediately becomes the new process hogging the cpu preventing the softlockup code from resetting the soft_watchdog_warn variable. This case is a false negative of "warn only once for a process", as there may be a different process that is going to hog the cpu. Resolve this by saving/checking the task pointer of the hogging process and use that to reset soft_watchdog_warn too. Signed-off-by: chai wen <chaiw.f...@cn.fujitsu.com> Signed-off-by: Don Zickus <dzic...@redhat.com> --- kernel/watchdog.c | 16 +++++++++++++++- 1 files changed, 15 insertions(+), 1 deletions(-) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 0037db6..2e55620 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -42,6 +42,7 @@ 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); #ifdef CONFIG_HARDLOCKUP_DETECTOR static DEFINE_PER_CPU(bool, hard_watchdog_warn); static DEFINE_PER_CPU(bool, watchdog_nmi_touch); @@ -328,8 +329,20 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) return HRTIMER_RESTART; /* only warn once */ - if (__this_cpu_read(soft_watchdog_warn) == true) + if (__this_cpu_read(soft_watchdog_warn) == true) { + /* + * Handle the case where multiple processes are + * causing softlockups but the duration is small + * enough, the softlockup detector can not reset + * itself in time. Use task pointers to detect this. + */ + if (__this_cpu_read(softlockup_task_ptr_saved) != + current) { + __this_cpu_write(soft_watchdog_warn, false); + __touch_watchdog(); + } return HRTIMER_RESTART; + } if (softlockup_all_cpu_backtrace) { /* Prevent multiple soft-lockup reports if one cpu is already @@ -345,6 +358,7 @@ 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) -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/