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

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Message-ID: <537EC8A5.8070508@oracle.com>
Date:	Fri, 23 May 2014 00:03:49 -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 05/22/2014 02:59 AM, Peter Zijlstra wrote:
> On Wed, May 21, 2014 at 10:34:44PM -0400, Sasha Levin wrote:
>> 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?
> 
> We do all that with preemption enabled, because its big and expensive,
> so its entirely possible that current (env->p) got moved around while we
> were doing it, at which point we'll look at it as a possible dst, while
> its already our src.

Seems to be working fine now, thanks!


Thanks,
Sasha

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