On 12/10/2007 09:19 AM, Gautham R Shenoy wrote: > commit 15bfb662b35c609490185fba2fd4713d230b9374 > Author: Gautham R Shenoy <[EMAIL PROTECTED]> > Date: Mon Dec 10 13:41:45 2007 +0530 > > softlockup: remove get_online_cpus() which doesn't help here. > > The get_online_cpus() protection seems to be bogus > in kernel/softlockup.c as cpu cached in check_cpu can go offline > once we do a put_online_cpus(). > > This can also cause deadlock during a cpu offline as follows: > > WATCHDOG_THREAD: OFFLINE_CPU: > mutex_down(&cpu_hotplug.lock); > /* All subsequent get_online_cpus > * will be blocked till we're > * done with this cpu-hotplug > * operation. > */ > > get_online_cpus(); > /* watchdog is blocked > Thus we cannot > go further until > the cpu-hotplug > operation completes > */ > CPU_DEAD: > kthread_stop(watchdog_thread); > > /* we're trying to stop a > * thread which is blocked > * waiting for us to finish. > * > * Since we cannot finish until > * the thread stops, we deadlock here! > */ > > Signed-off-by: Gautham R Shenoy <[EMAIL PROTECTED]> > Cc: Ingo Molnar <[EMAIL PROTECTED]> > Cc: Thomas Gleixner <[EMAIL PROTECTED]> > Cc: Arjan van de Van <[EMAIL PROTECTED]> > Cc: Jiri Slaby <[EMAIL PROTECTED]>
Tested-by: Jiri Slaby <[EMAIL PROTECTED]> > diff --git a/kernel/softlockup.c b/kernel/softlockup.c > index e50b44a..576eb9c 100644 > --- a/kernel/softlockup.c > +++ b/kernel/softlockup.c > @@ -219,9 +219,7 @@ static int watchdog(void *__bind_cpu) > /* > * Only do the hung-tasks check on one CPU: > */ > - get_online_cpus(); > check_cpu = any_online_cpu(cpu_online_map); > - put_online_cpus(); > > if (this_cpu != check_cpu) > continue; > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
