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Date:	Wed, 21 May 2014 22:34:44 -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 05/21/2014 12:49 PM, Peter Zijlstra wrote:
> On Wed, May 21, 2014 at 03:19:48PM +0200, Peter Zijlstra wrote:
>> > On Wed, May 21, 2014 at 09:08:26AM -0400, Sasha Levin wrote:
>>> > > +++ 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?
>> > 
>> > Oi, good call that, lemme go stare.
> I think something simple like this should be sufficient to avoid the
> problem of selecting oneself as a flip target.

Why would that happen in the first place?


Thanks,
Sasha
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