linux-kernel - Re: [PATCH pm-freezer 1/4] cgroup_freezer: fix freezer->state setting bug in freezer_change

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Message-ID: <20110902173039.GA9039@redhat.com>
Date:	Fri, 2 Sep 2011 19:30:39 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Matt Helsley <matthltc@...ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Paul Menage <paul@...lmenage.org>,
	containers@...ts.linux-foundation.org,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH pm-freezer 1/4] cgroup_freezer: fix freezer->state
	setting bug in freezer_change_state()

On 09/03, Tejun Heo wrote:
>
> Can you please wait a bit?

Sure. But just in case, I mean the simple patch below.

Feel free to incorporate into 4/4, or I can resend it later.

Oleg.

------------------------------------------------------------------------------
[PATCH] freezer: remove the pointless/unsafe __thaw_task()->recalc_sigpending_and_wake()

Remove __thaw_task()->recalc_sigpending_and_wake(). It was copied from
cancel_freezing() recently, but it was always wrong.

It is pointless, contary to the comment it can't clear TIF_SIGPENDING.
Not to mention, we must never do this with !current task, this is wrong.

The usage of ->sighand is not safe if the caller is cgroup_freezer, we
can racw with exit.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---

 kernel/freezer.c |   10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

--- 3.1/kernel/freezer.c~kill_rspaw	2011-09-02 18:52:46.000000000 +0200
+++ 3.1/kernel/freezer.c	2011-09-02 19:03:30.000000000 +0200
@@ -150,18 +150,10 @@ void __thaw_task(struct task_struct *p)
 	 * be visible to @p as waking up implies wmb.  Waking up inside
 	 * freezer_lock also prevents wakeups from leaking outside
 	 * refrigerator.
-	 *
-	 * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
-	 * avoid leaving dangling TIF_SIGPENDING behind.
 	 */
 	spin_lock_irqsave(&freezer_lock, flags);
-	if (frozen(p)) {
+	if (frozen(p))
 		wake_up_process(p);
-	} else {
-		spin_lock(&p->sighand->siglock);
-		recalc_sigpending_and_wake(p);
-		spin_unlock(&p->sighand->siglock);
-	}
 	spin_unlock_irqrestore(&freezer_lock, flags);
 }
 

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