linux-kernel - Re: [PATCH pm-for-3.2 2/2] freezer: revert 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK

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Message-ID: <20111104001759.GU4417@google.com>
Date:	Thu, 3 Nov 2011 17:17:59 -0700
From:	Tejun Heo <tj@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>,
	Jeff Layton <jlayton@...hat.com>
Subject: Re: [PATCH pm-for-3.2 2/2] freezer: revert 27920651fe "PM /
 Freezer: Make fake_signal_wake_up() wake TASK_KILLABLE tasks too"

Hello, Rafael.

On Fri, Nov 04, 2011 at 01:13:21AM +0100, Rafael J. Wysocki wrote:
> On Friday, November 04, 2011, Tejun Heo wrote:
> > Commit 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake
> > TASK_KILLABLE tasks too" updated fake_signal_wake_up() used by freezer
> > to wake up KILLABLE tasks.  Sending unsolicited wakeups to tasks in
> > killable sleep is dangerous as there are code paths which depend on
> > tasks not waking up spuriously from KILLABLE sleep.
> > 
> > For example. sys_read() or page can sleep in TASK_KILLABLE assuming
> > that wait/down/whatever _killable can only fail if we can not return
> > to the usermode.  TASK_TRACED is another obvious example.
> > 
> > The previous patch updated wait_event_freezekillable() such that it
> > doesn't depend on the spurious wakeup.  This patch reverts the
> > offending commit.
> > 
> > Note that the spurious KILLABLE wakeup had other implicit effects in
> > KILLABLE sleeps in nfs and cifs and those will need further updates to
> > regain freezekillable behavior.
> > 
> > Signed-off-by: Tejun Heo <tj@...nel.org>
> > Cc: Jeff Layton <jlayton@...hat.com>
> > LKML-Reference: <20111031221743.GA18855@...gle.com>
> 
> Applied to linux-pm/linux-next.

Just to be sure, as the commit which changed fake_signal_wake_up() to
use KILLABLE wakeup is already mainline, these two will have to be
pushed as fixes after some time in this devel cycle.

Thanks.

-- 
tejun
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