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: <201111040124.34015.rjw@sisk.pl>
Date:	Fri, 4 Nov 2011 01:24:33 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Tejun Heo <tj@...nel.org>
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"

On Friday, November 04, 2011, Tejun Heo wrote:
> 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.

Yes, they are 3.2 material and I'm going to push them in the next few days
along with a number of other PM-related fixes/cleanups.  Is that OK?

Rafael
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