linux-kernel - Re: [Update][PATCH] PM / Hibernate: Fix s2disk regression related to unlock_system

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Message-ID: <20120118220444.GB21533@google.com>
Date:	Wed, 18 Jan 2012 14:04:44 -0800
From:	Tejun Heo <tj@...nel.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, horms@...ge.net.au,
	"pavel@....cz" <pavel@....cz>, Len Brown <lenb@...nel.org>
Subject: Re: [Update][PATCH] PM / Hibernate: Fix s2disk regression related
 to unlock_system_sleep()

On Thu, Jan 19, 2012 at 01:59:01AM +0530, Srivatsa S. Bhat wrote:
> From: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> Subject: [PATCH] PM / Hibernate: Rewrite unlock_system_sleep() to fix s2disk regression
> 
> Commit 33e638b, "PM / Sleep: Use the freezer_count() functions in
> [un]lock_system_sleep() APIs" introduced an undesirable change in the
> behaviour of unlock_system_sleep() since freezer_count() internally calls
> try_to_freeze() - which we don't need in unlock_system_sleep().
> 
> And commit bcda53f, "PM / Sleep: Replace mutex_[un]lock(&pm_mutex) with
> [un]lock_system_sleep()" made these APIs wide-spread. This caused a
> regression in suspend-to-disk where snapshot_read() and snapshot_write()
> were getting frozen due to the try_to_freeze embedded in
> unlock_system_sleep(), since these functions were invoked when the freezing
> condition was still in effect.
> 
> Fix this by rewriting unlock_system_sleep() by open-coding freezer_count()
> and dropping the try_to_freeze() part. Not only will this fix the
> regression but this will also ensure that the API only does what it is
> intended to do, and nothing more, under the hood.
> 
> While at it, make the code more correct and robust by ensuring that the
> PF_FREEZER_SKIP flag gets cleared with pm_mutex held, to avoid a race with
> the freezer.
> 
> Reported-by: Rafael J. Wysocki <rjw@...k.pl>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks!

-- 
tejun
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