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

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Message-ID: <alpine.LFD.2.02.1207161058550.32033@ionos>
Date:	Mon, 16 Jul 2012 10:59:46 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mike Galbraith <mgalbraith@...ell.com>
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
Subject: Re: Deadlocks due to per-process plugging

On Mon, 16 Jul 2012, Mike Galbraith wrote:
> On Sun, 2012-07-15 at 11:14 +0200, Mike Galbraith wrote: 
> > On Sun, 2012-07-15 at 10:59 +0200, Thomas Gleixner wrote: 
> 
> > > Can you figure out on which lock the stuck thread which did not unplug
> > > due to tsk_is_pi_blocked was blocked?
> > 
> > I'll take a peek.
> 
> Sorry for late reply, took a half day away from box.  Jan had already
> done the full ext3 IO deadlock analysis:
> 
> Again kjournald is waiting for buffer IO on block 4367635 (sector
> 78364838) to finish.  Now it is dbench thread 0xffff88026f330e70 which
> has submitted this buffer for IO and is still holding this buffer behind
> its plug (request for sector 78364822..78364846). The dbench thread is
> waiting on j_checkpoint mutex (apparently it has successfully got the
> mutex in the past, checkpointed some buffers, released the mutex and
> hung when trying to acquire it again in the next loop of
> __log_wait_for_space()). 

And what's holding j_checkpoint mutex and not making progress?

Thanks,

	tglx
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