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SubjectRe: Intermittent early panic in try_to_wake_up
Mike Galbraith wrote:
> On Thu, 2009-10-22 at 20:33 -0300, Kevin Winchester wrote:
>> Hi,
>>
>> A week or two ago I saw a panic on boot in try_to_wake_up, but it was not
>> reproducible and I had not written down any trace information. This
>> evening I saw it twice more, but then on the third boot things worked fine.
>> This time I copied down the stack trace:
>>
>> try_to_wake_up+0x2e/0x102
>> wake_up_process+0x10/0x12
>> kthread_create+0x88/0x12c
>> ?ksoftirqd+0x00/0xb7
>> cpu_callback+0x42/0x8f
>> ?spawn_ksoftirqd+0x0/0x39
>> spawn_ksoftirqd+0x17/0x39
>> do_one_initcall+0x58/0x147
>>
>> The first time it happened, I remember checking the git logs and it was
>> shortly after:
>>
>> commit f5dc37530ba8a35aae0f7f4f13781d1904f71e94
>> Author: Mike Galbraith <efault@gmx.de>
>> Date: Fri Oct 9 08:35:03 2009 +0200
>>
>> sched: Update the clock of runqueue select_task_rq() selected
>>
>> In try_to_wake_up(), we update the runqueue clock, but
>> select_task_rq() may select a different runqueue than the one we
>> updated, leaving the new runqueue's clock stale for a bit.
>>
>> This patch cures occasional huge latencies reported by latencytop
>> when coming out of idle on a mostly idle NO_HZ box.
>>
>> Signed-off-by: Mike Galbraith <efault@gmx.de>
>> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
>> LKML-Reference: <1255070103.7639.30.camel@marge.simson.net>
>> Signed-off-by: Ingo Molnar <mingo@elte.hu>
>>
>>
>> ...so perhaps that has something to do with it.
>
> I don't think that's very likely. Box did explode near my grubby
> fingerprints though.
>
>> Config below. Any help would be appreciated.
>
> Building with your config, try_to_wake_up+0x2e is around..
>
> (gdb) list *try_to_wake_up+0x2e
> 0xffffffff81029107 is in try_to_wake_up (kernel/sched.c:2324).
> 2319 this_cpu = get_cpu();
> 2320
> 2321 smp_wmb();
> 2322 rq = orig_rq = task_rq_lock(p, &flags);
> 2323 update_rq_clock(rq);
> 2324 if (!(p->state & state))
> 2325 goto out;
> 2326
> 2327 if (p->se.on_rq)
> 2328 goto out_running;
>
> I don't see how any of that can explode without something very bad
> having happened to ksoftirqd before we tried to wake it.
>

I thought this problem had solved itself, but I've hit it again three times
in the last few days.

I've expanded the CC list a little (based on get_maintainer for
kernel/softirq.c, since that seems to be involved somehow, and Rafael since
this definitely seems to be a regression), to see if anyone else has any
ideas.

--
Kevin Winchester



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