Re: Linux 3.19-rc3

Chris Mason
2015-01-16T17:00:54Z

On Fri, Jan 16, 2015 at 11:56 AM, Peter Hurley
<peter@hurleysoftware.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@infradead.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