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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Date:	Fri, 4 Nov 2011 01:13:21 +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:
> 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.

Thanks,
Rafael


> ---
> This will cause conflict with the pending linux-next patches but the
> resolution should be trivial.  Simply changing @resume from 0 to 1 is
> enough.
> 
> Thanks.
> 
>  kernel/freezer.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: work/kernel/freezer.c
> ===================================================================
> --- work.orig/kernel/freezer.c
> +++ work/kernel/freezer.c
> @@ -67,7 +67,7 @@ static void fake_signal_wake_up(struct t
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&p->sighand->siglock, flags);
> -	signal_wake_up(p, 1);
> +	signal_wake_up(p, 0);
>  	spin_unlock_irqrestore(&p->sighand->siglock, flags);
>  }
>  
> 
> 

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