Re: Intermittent early panic in try_to_wake_up

From: Mike Galbraith
Date: Fri Oct 23 2009 - 05:23:12 EST


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@xxxxxx>
> 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@xxxxxx>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> LKML-Reference: <1255070103.7639.30.camel@xxxxxxxxxxxxxxxx>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
>
>
> ...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.

-Mike

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