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

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Date:	Sun, 15 Jul 2012 11:51:22 +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 Sun, 15 Jul 2012, Mike Galbraith wrote:

> On Sun, 2012-07-15 at 10:59 +0200, Thomas Gleixner wrote: 
> > On Fri, 13 Jul 2012, Jan Kara wrote:
> > > On Fri 13-07-12 16:25:05, Thomas Gleixner wrote:
> > > > So the patch below should allow the unplug to take place when blocked
> > > > on mutexes etc.
> > >   Thanks for the patch! Mike will give it some testing.
> > 
> > I just found out that this patch will explode nicely when the unplug
> > code runs into a contended lock. Then we try to block on that lock and
> > make the rtmutex code unhappy as we are already blocked on something
> > else.
> 
> Kinda like so?  My x3550 M3 just exploded.  Aw poo. 

Yep. Would have surprised me if it never triggered.

> > So no, it's not a solution to the problem. Sigh.
> > 
> > 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.

Thanks!
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