linux-kernel - [PATCH 4/6] freezer: use lock_task_sighand() in fake_signal_wake

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Message-Id: <1314988070-12244-5-git-send-email-tj@kernel.org>
Date:	Sat,  3 Sep 2011 03:27:48 +0900
From:	Tejun Heo <tj@...nel.org>
To:	oleg@...hat.com, matthltc@...ibm.com, rjw@...k.pl,
	paul@...lmenage.org
Cc:	containers@...ts.linux-foundation.org,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 4/6] freezer: use lock_task_sighand() in fake_signal_wake_up()

cgroup_freezer calls freeze_task() without holding tasklist_lock and,
if the task is exiting, its ->sighand may be gone by the time
fake_signal_wake_up() is called.  Use lock_task_sighand() instead of
accessing ->sighand directly.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Oleg Nesterov <oleg@...hat.com>
Cc: "Rafael J. Wysocki" <rjw@...k.pl>
Cc: Paul Menage <paul@...lmenage.org>
---
 kernel/freezer.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/freezer.c b/kernel/freezer.c
index ebee1ab..9846133 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -93,9 +93,10 @@ static void fake_signal_wake_up(struct task_struct *p)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&p->sighand->siglock, flags);
-	signal_wake_up(p, 0);
-	spin_unlock_irqrestore(&p->sighand->siglock, flags);
+	if (lock_task_sighand(p, &flags)) {
+		signal_wake_up(p, 0);
+		unlock_task_sighand(p, &flags);
+	}
 }
 
 /**
-- 
1.7.6

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