linux-kernel - Re: Linux 3.19-rc3

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Message-ID: <20150106110112.GQ29390@twins.programming.kicks-ass.net>
Date:	Tue, 6 Jan 2015 12:01:12 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sedat Dilek <sedat.dilek@...il.com>
Cc:	Dave Jones <davej@...emonkey.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Kent Overstreet <kmo@...erainc.com>, Chris Mason <clm@...com>
Subject: Re: Linux 3.19-rc3

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.
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