linux-kernel - Re: Linux 3.19-rc5

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Date:	Wed, 21 Jan 2015 14:12:00 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	tglx@...utronix.de, ilya.dryomov@...tank.com,
	umgwanakikbuti@...il.com, oleg@...hat.com
Subject: Re: Linux 3.19-rc5

On Wed, 2015-01-21 at 22:37 +0100, Bruno Prémont wrote:
> On Wed, 21 January 2015 Bruno Prémont wrote:
> > On Tue, 20 January 2015 Linus Torvalds wrote:
> > > On Tue, Jan 20, 2015 at 6:02 AM, Bruno Prémont wrote:
> > > >
> > > > No idea yet which rc is the offender (nor exact patch), but on my not
> > > > so recent UP laptop with a pccard slot I have 2 pccardd kernel threads
> > > > converting my laptop into a heater.
> > > >
> > > > lspci for affected nodes:
> > > > 02:06.0 CardBus bridge [0607]: O2 Micro, Inc. OZ711EC1 SmartCardBus Controller [1217:7113] (rev 20)
> > > > 02:06.1 CardBus bridge [0607]: O2 Micro, Inc. OZ711EC1 SmartCardBus Controller [1217:7113] (rev 20)
> > > >
> > > > Very basics I have, before I attempt any bisection:
> > > 
> > > Hmm. I'm not seeing anything recent changing anything in this area, so
> > > I suspect that unless somebody else steps up and says "Ahh, that
> > > sounds like xyz", your bisection is the best option.
> 
> Bisecting to the end did point me at (the warning traces produced in great
> quantities might not be the very same issue as the abusive CPU usage, but
> certainly look very related):
>   [CCing people on CC for the patch]
> 
> commit 8eb23b9f35aae413140d3fda766a98092c21e9b0
> Author: Peter Zijlstra <peterz@...radead.org>
> Date:   Wed Sep 24 10:18:55 2014 +0200
> 
>     sched: Debug nested sleeps
>     
>     Validate we call might_sleep() with TASK_RUNNING, which catches places
>     where we nest blocking primitives, eg. mutex usage in a wait loop.
>     
>     Since all blocking is arranged through task_struct::state, nesting
>     this will cause the inner primitive to set TASK_RUNNING and the outer
>     will thus not block.
>     
>     Another observed problem is calling a blocking function from
>     schedule()->sched_submit_work()->blk_schedule_flush_plug() which will
>     then destroy the task state for the actual __schedule() call that
>     comes after it.
>     
>     Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>     Cc: tglx@...utronix.de
>     Cc: ilya.dryomov@...tank.com
>     Cc: umgwanakikbuti@...il.com
>     Cc: oleg@...hat.com
>     Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>     Link: http://lkml.kernel.org/r/20140924082242.591637616@infradead.org
>     Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> Which does produce the following trace (hand-copied most important parts of it):
>   Warning: CPU 0 PID: 68 at kernel/sched/core.c:7311 __might_sleep+0x143/0x170
>   do not call blocking ops when !TASK_RUNNING; state=1 set at [<c1436390>] pccardd+0xa0/0x3e0
>   ...
>   Call trace:
>     ...
>     __might_sleep+0x143/0x170
>     ? pccardd+0xa0/0x3e0
>     ? pccardd+0xa0/0x3e0
>     mutex_lock+0x17/0x2a
>     pccardd+0xe9/0x3e0
>     ? pcmcia_socket_uevent+0x30/0x30
> 
> pccardd() is located in drivers/pcmcia/cs.c and seems to be of the structure
> Peter's patch wants to warn about.

Yeah setting current to interruptable so early in the game is bogus. It
should be set after unlocking the skt_mutex.

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