linux-kernel - [PATCH] rcu_tree: avoid touch rnp->completed when starts a new GP

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Date:	Tue, 13 Jan 2015 15:30:34 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	<linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
CC:	Lai Jiangshan <laijs@...fujitsu.com>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [PATCH] rcu_tree: avoid touch rnp->completed when starts a new GP

In rcu_gp_init(), rnp->completed equals to rsp->completed in THEORY,
we don't need to touch it normally.  If something goes wrong,
it will complain and fixup rnp->completed and avoid oops.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
 kernel/rcu/tree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 7680fc2..ea6dc28 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1639,8 +1639,8 @@ static int rcu_gp_init(struct rcu_state *rsp)
 		rcu_preempt_check_blocked_tasks(rnp);
 		rnp->qsmask = rnp->qsmaskinit;
 		ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;
-		WARN_ON_ONCE(rnp->completed != rsp->completed);
-		ACCESS_ONCE(rnp->completed) = rsp->completed;
+		if (WARN_ON_ONCE(rnp->completed != rsp->completed))
+			ACCESS_ONCE(rnp->completed) = rsp->completed;
 		if (rnp == rdp->mynode)
 			(void)__note_gp_changes(rsp, rnp, rdp);
 		rcu_preempt_boost_start_gp(rnp);
-- 
2.1.0

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