linux-kernel - Re: Freezable workqueue blocks non-freezable workqueue during the system resume process

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Message-ID: <20160226061920.GA17288@shlinux2.ap.freescale.net>
Date:	Fri, 26 Feb 2016 14:19:20 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Alan Stern <stern@...land.harvard.edu>, florian@...kler.org,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	usb-storage@...ts.one-eyed-alien.net
Subject: Re: Freezable workqueue blocks non-freezable workqueue during the
 system resume process

On Thu, Feb 25, 2016 at 05:01:12PM -0500, Tejun Heo wrote:
> Hello, Peter.
> 
> On Wed, Feb 24, 2016 at 03:24:30PM +0800, Peter Chen wrote:
> > > You might want to complain to the block-layer people about this.  I 
> > > don't know if anything can be done to fix it.
> > > 
> > > Or maybe flush_work and flush_delayed_work can be changed to avoid 
> > > blocking if the workqueue is frozen.  Tejun?
> > > 
> > 
> > I have a patch to show the root cause of this issue.
> > 
> > http://www.spinics.net/lists/linux-usb/msg136815.html
> 
> I don't get it.  Why would it deadlock?  Shouldn't things get rolling
> once the workqueues are thawed?
> 

Hi Tejun,

The workqueue writeback can't be thawed due to driver's resume
(dpm_complete) is lock nested, and can't be finished.

-- 

Best Regards,
Peter Chen