Re: Intermittent early panic in try_to_wake_up

From: Kevin Winchester
Date: Thu Nov 05 2009 - 18:42:12 EST

Mike Galbraith wrote:
On Thu, 2009-10-22 at 20:33 -0300, Kevin Winchester wrote:

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:


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> 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();
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;
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

Kevin Winchester

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