The patch titled Subject: softlockup: make detector be aware of task switch of processes hogging cpu has been added to the -mm tree. Its filename is softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: chai wen <chaiw.fnst@xxxxxxxxxxxxxx> Subject: softlockup: make detector be aware of task switch of processes hogging cpu 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.fnst@xxxxxxxxxxxxxx> Signed-off-by: Don Zickus <dzickus@xxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/watchdog.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff -puN kernel/watchdog.c~softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu kernel/watchdog.c --- a/kernel/watchdog.c~softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu +++ a/kernel/watchdog.c @@ -47,6 +47,7 @@ static DEFINE_PER_CPU(bool, softlockup_t 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); @@ -333,8 +334,20 @@ static enum hrtimer_restart watchdog_tim 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 @@ -350,6 +363,7 @@ static enum hrtimer_restart watchdog_tim 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) _ Patches currently in -mm which might be from chaiw.fnst@xxxxxxxxxxxxxx are softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch linux-next.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html