linux-kernel - [PATCH tip/core/rcu 2/3] rcu: suppress __mpol

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Date:	Wed,  3 Mar 2010 17:50:17 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>
Subject: [PATCH tip/core/rcu 2/3] rcu: suppress __mpol_dup() false positive from RCU lockdep

Common code is used during task creation and after the task has started
running.  RCU protection is not needed during task creation because no
other CPU has access to the under-construction task.  Provide the RCU
protection anyway to suppress the false positive, as there does not
appear to be a good way for the common code to recognize that the task
is only accessible to the CPU creating it.

Cc: Paul Menage <menage@...gle.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 mm/mempolicy.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 290fb5b..3cec080 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1730,10 +1730,12 @@ struct mempolicy *__mpol_dup(struct mempolicy *old)
 
 	if (!new)
 		return ERR_PTR(-ENOMEM);
+	rcu_read_lock();
 	if (current_cpuset_is_being_rebound()) {
 		nodemask_t mems = cpuset_mems_allowed(current);
 		mpol_rebind_policy(old, &mems);
 	}
+	rcu_read_unlock();
 	*new = *old;
 	atomic_set(&new->refcnt, 1);
 	return new;
-- 
1.6.6

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