linux-kernel - [tip:core/urgent] rcu: Fix RCU lockdep splat on freezer

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Message-ID: <tip-8b46f880841aac821af8efa6581bb0e46b8b9845@git.kernel.org>
Date:	Fri, 30 Apr 2010 10:51:54 GMT
From:	"tip-bot for Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	hpa@...or.com, mingo@...hat.com, lizf@...fujitsu.com,
	eparis@...isplace.org, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:core/urgent] rcu: Fix RCU lockdep splat on freezer_fork path

Commit-ID:  8b46f880841aac821af8efa6581bb0e46b8b9845
Gitweb:     http://git.kernel.org/tip/8b46f880841aac821af8efa6581bb0e46b8b9845
Author:     Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
AuthorDate: Wed, 21 Apr 2010 13:02:08 -0700
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 30 Apr 2010 12:03:17 +0200

rcu: Fix RCU lockdep splat on freezer_fork path

Add an RCU read-side critical section to suppress this false
positive.

Located-by: Eric Paris <eparis@...isplace.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Acked-by: Li Zefan <lizf@...fujitsu.com>
Cc: laijs@...fujitsu.com
Cc: dipankar@...ibm.com
Cc: mathieu.desnoyers@...ymtl.ca
Cc: josh@...htriplett.org
Cc: dvhltc@...ibm.com
Cc: niv@...ibm.com
Cc: peterz@...radead.org
Cc: rostedt@...dmis.org
Cc: Valdis.Kletnieks@...edu
Cc: dhowells@...hat.com
Cc: eric.dumazet@...il.com
LKML-Reference: <1271880131-3951-2-git-send-email-paulmck@...ux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/cgroup_freezer.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index da5e139..e5c0244 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -205,9 +205,12 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
 	 * No lock is needed, since the task isn't on tasklist yet,
 	 * so it can't be moved to another cgroup, which means the
 	 * freezer won't be removed and will be valid during this
-	 * function call.
+	 * function call.  Nevertheless, apply RCU read-side critical
+	 * section to suppress RCU lockdep false positives.
 	 */
+	rcu_read_lock();
 	freezer = task_freezer(task);
+	rcu_read_unlock();
 
 	/*
 	 * The root cgroup is non-freezable, so we can skip the
--
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