linux-kernel - Re: [linux-pm] Is it supposed to be ok to call del

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Date:	Fri, 23 Apr 2010 07:17:07 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Matt Reimer <mattjreimer@...il.com>
Cc:	"linux-kernel" <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Jens Axboe <jens.axboe@...cle.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	"linux-pm" <linux-pm@...ts.linux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>
Subject: Re: [linux-pm] Is it supposed to be ok to call del_gendisk while userspace is frozen?

On Friday 23 April 2010, Matt Reimer wrote:
> On Thu, Mar 4, 2010 at 1:15 PM, Pavel Machek <pavel@....cz> wrote:
> > Hi!
> >
> >> > My thought exactly.  This is the only approach that also solves the
> >> > following race:
> >> >
> >> >     A driver is unloaded at the same time as a suspend starts.
> >> >
> >> >     The writeback thread gets frozen.
> >> >
> >> >     Then before the rmmod thread is frozen, it calls del_gendisk.
> >> >
> >> > Delaying things by means of a workqueue (or the equivalent) might also
> >> > work, but it doesn't seem as safe.  For example, some important
> >> > writebacks might end up getting delayed until too late.
> >
> > Delaying writebacks during sleep should be ok... That's why we do
> > sync() after userspace is frozen -- nothing really important should be
> > waiting for writeback after that point.
> 
> Has this been fixed,

No, it hasn't.

> or has a consensus about how to fix this been
> achieved? I'm hitting the same problem and have some time to work on a
> fix.

Generally, it looks like del_gendisk should thaw writeback threads, but not
during suspend, only during resume.

Rafael
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