Re: Linux 3.19-rc3

[Chris Mason]

On Fri, Jan 16, 2015 at 11:56 AM, Peter Hurley 
<peter@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> 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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