From: Jan Kara <jack@suse.cz>
To: Tejun Heo <tj@kernel.org>
Cc: Peter Chen <hzpeterchen@gmail.com>,
Alan Stern <stern@rowland.harvard.edu>,
florian@mickler.org, linux-usb@vger.kernel.org,
linux-kernel@vger.kernel.org,
usb-storage@lists.one-eyed-alien.net, Jan Kara <jack@suse.com>,
jkosina@suse.cz
Subject: Re: Freezable workqueue blocks non-freezable workqueue during the system resume process
Date: Thu, 3 Mar 2016 10:33:10 +0100 [thread overview]
Message-ID: <20160303093310.GC2307@quack.suse.cz> (raw)
In-Reply-To: <20160302160058.GA29826@mtj.duckdns.org>
Hello,
On Wed 02-03-16 11:00:58, Tejun Heo wrote:
> On Fri, Feb 26, 2016 at 02:19:20PM +0800, Peter Chen wrote:
> > 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?
> >
> > The workqueue writeback can't be thawed due to driver's resume
> > (dpm_complete) is lock nested, and can't be finished.
>
> Ugh... that's nasty. I wonder whether the right thing to do is making
> writeback workers non-freezable. IOs are supposed to be blocked from
> lower layer anyway. Jan, what do you think?
Well no, at least currently IO is not blocked in lower layers AFAIK - for
that you'd need to freeze block devices & filesystems and there are issues
with that (Jiri Kosina was the last one which was trying to make this work
AFAIR). And I think you need to stop writeback (and generally any IO) to be
generated so that it doesn't interact in a strange way with device drivers
being frozen. So IMO until suspend freezes filesystems & devices properly
you have to freeze writeback workqueue.
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2016-03-03 9:32 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-23 3:20 Freezable workqueue blocks non-freezable workqueue during the system resume process Peter Chen
2016-02-23 9:47 ` Peter Chen
2016-02-23 15:34 ` Alan Stern
2016-02-24 7:24 ` Peter Chen
2016-02-25 22:01 ` Tejun Heo
2016-02-26 6:19 ` Peter Chen
2016-03-02 16:00 ` Tejun Heo
2016-03-03 9:33 ` Jan Kara [this message]
2016-03-11 17:56 ` Tejun Heo
2016-03-14 7:22 ` Jan Kara
2016-03-14 14:37 ` Alan Stern
2016-03-15 9:25 ` Jan Kara
2016-03-16 15:00 ` Tejun Heo
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