linux-kernel - Re: [RFC PATCH] fs: Use a seperate wq for do_sync

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Message-ID: <20140919154423.GH25400@atomlin.usersys.redhat.com>
Date:	Fri, 19 Sep 2014 16:44:23 +0100
From:	Aaron Tomlin <atomlin@...hat.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, linux-fsdevel@...r.kernel.org,
	viro@...iv.linux.org.uk, bmr@...hat.com, jcastillo@...hat.com,
	mguzik@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] fs: Use a seperate wq for do_sync_work() to avoid a
 potential deadlock

On Thu, Sep 18, 2014 at 07:16:13AM +1000, Dave Chinner wrote:
> >   - Both lru_add_drain and do_sync_work work items are added to
> >     the same global system_wq
> > 
> >   - The current work fn on the system_wq is do_sync_work and is
> >     blocked waiting to aquire an sb's s_umount for reading
> > 
> >   - The umount task is the current owner of the s_umount in
> >     question but is waiting for do_sync_work to continue.
> >     Thus we hit a deadlock situation.
> 
> What kernel did you see this deadlock on?

Sorry for the noise. This deadlock was produced under a kernel whereby
the workqueue implementation is significantly less sophisticated.

-- 
Aaron Tomlin
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