linux-kernel - Re: sched: spinlock recursion in migrate_swap

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Date:	Wed, 21 May 2014 09:08:26 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Dave Jones <davej@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: sched: spinlock recursion in migrate_swap_stop

On 05/20/2014 09:03 AM, Sasha Levin wrote:
> On 05/20/2014 07:04 AM, Peter Zijlstra wrote:
>> > On Mon, May 19, 2014 at 10:05:31PM -0400, Sasha Levin wrote:
>>> >> ping? It seems to be easy enough to reproduce on -next, I'd be happy to try
>>> >> debug patches/fixes.
>> > 
>> > Does this fuzzing you do also include hotplug? If so, does disabling
>> > that make this problem go away?
>> > 
> There were no hotplug operations going on when this happens, so it seems
> unrelated.

I've added a small test:

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 927fa33..b5e11c7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1154,6 +1156,7 @@ int migrate_swap(struct task_struct *cur, struct task_struct *p)
                goto out;

        trace_sched_swap_numa(cur, arg.src_cpu, p, arg.dst_cpu);
+       BUG_ON(cur == p);
        ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);

 out:


Which seems to get hit. This sounds like a race with task moving to
other cpu maybe?


Thanks,
Sasha
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