linux-kernel - Re: Deadlocks due to per-process plugging

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Message-ID: <1342856835.7739.19.camel@marge.simpson.net>
Date:	Sat, 21 Jul 2012 09:47:15 +0200
From:	Mike Galbraith <efault@....de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Jan Kara <jack@...e.cz>, Jeff Moyer <jmoyer@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Jens Axboe <jaxboe@...ionio.com>, mgalbraith@...e.com,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: Deadlocks due to per-process plugging

On Wed, 2012-07-18 at 07:30 +0200, Mike Galbraith wrote: 
> On Wed, 2012-07-18 at 06:44 +0200, Mike Galbraith wrote:
> 
> > The patch in question for missing Cc.  Maybe should be only mutex, but I
> > see no reason why IO dependency can only possibly exist for mutexes...
> 
> Well that was easy, box quickly said "nope, mutex only does NOT cut it".

And I also learned (ouch) that both doesn't cut it either.  Ksoftirqd
(or sirq-blk) being nailed by q->lock in blk_done_softirq() is.. not
particularly wonderful.  As long as that doesn't happen, IO deadlock
doesn't happen, troublesome filesystems just work.  If it does happen
though, you've instantly got a problem.

-Mike

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