linux-kernel - Re: Linux 3.19-rc3

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Date:	Fri, 16 Jan 2015 12:00:07 -0500
From:	Chris Mason <clm@...com>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	Kent Overstreet <kmo@...erainc.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Dave Jones <davej@...emonkey.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Linux 3.19-rc3

On Fri, Jan 16, 2015 at 11:56 AM, Peter Hurley 
<peter@...leysoftware.com> wrote:
> On 01/06/2015 06:07 AM, Kent Overstreet wrote:
>>  On Tue, Jan 06, 2015 at 12:01:12PM +0100, Peter Zijlstra wrote:
>>>  On Tue, Jan 06, 2015 at 11:18:04AM +0100, Sedat Dilek wrote:
>>>>  On Tue, Jan 6, 2015 at 11:06 AM, Peter Zijlstra 
>>>> <peterz@...radead.org> wrote:
>>>>>  On Tue, Jan 06, 2015 at 10:57:19AM +0100, Sedat Dilek wrote:
>>>>>>  [   88.028739]  [<ffffffff8124433f>] aio_read_events+0x4f/0x2d0
>>>>>> 
>>>>> 
>>>>>  Ah, that one. Chris Mason and Kent Overstreet were looking at 
>>>>> that one.
>>>>>  I'm not touching the AIO code either ;-)
>>>> 
>>>>  I know, I was so excited when I see nearly the same output.
>>>> 
>>>>  Can you tell me why people see "similiar" problems in different 
>>>> areas?
>>> 
>>>  Because the debug check is new :-) It's a pattern that should not 
>>> be
>>>  used but mostly works most of the times.
>>> 
>>>>  [  181.397024] WARNING: CPU: 0 PID: 2872 at 
>>>> kernel/sched/core.c:7303
>>>>  __might_sleep+0xbd/0xd0()
>>>>  [  181.397028] do not call blocking ops when !TASK_RUNNING; 
>>>> state=1
>>>>  set at [<ffffffff810b83bd>] prepare_to_wait_event+0x5d/0x110
>>>> 
>>>>  With similiar buzzwords... namely...
>>>> 
>>>>  mutex_lock_nested
>>>>  prepare_to_wait(_event)
>>>>  __might_sleep
>>>> 
>>>>  I am asking myself... Where is the real root cause - in 
>>>> sched/core?
>>>>  Fix one single place VS. fix the impact at several other places?
>>> 
>>>  No, the root cause is nesting sleep primitives, this is not 
>>> fixable in
>>>  the one place, both prepare_to_wait and mutex_lock are using
>>>  task_struct::state, they have to, no way around it.
>> 
>>  No, it's completely possible to construct a prepare_to_wait() that 
>> doesn't
>>  require messing with the task state. Had it for years.
>> 
>>  
>> https://urldefense.proofpoint.com/v1/url?u=http://evilpiepirate.org/git/linux-bcache.git/log/?h%3Daio_ring_fix&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=6%2FL0lzzDhu0Y1hL9xm%2BQyA%3D%3D%0A&m=QKQw1WQ3qeio%2FM623F%2BN1X1PeHp7PLLjdIQdHnHU5qo%3D%0A&s=b4e94a6a4b0922e356cadd19f6b22862dbd258fa11c2f26c3d7d76dcac1963ce
> 
> Peter & Kent,
> 
> What's the plan here?

I'm cleaning up my patch slightly and resubmitting.

-chris



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