linux-kernel - [RFC PATCH] rcu: using ACCESS_ONCE() to observe the jiffies

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Date:	Tue, 28 Sep 2010 16:32:43 +0800
From:	Dongdong Deng <dongdong.deng@...driver.com>
To:	paulmck@...ux.vnet.ibm.com, dipankar@...ibm.com
Cc:	linux-kernel@...r.kernel.org, dongdong.deng@...driver.com
Subject: [RFC PATCH] rcu: using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value

Using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
due to the caller didn't hold the root_rcu/rnp node's lock.

Signed-off-by: Dongdong Deng <dongdong.deng@...driver.com>
CC: Dipankar Sarma <dipankar@...ibm.com>
CC: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d5bc439..07a7063 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -532,9 +532,9 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
 
 	if (rcu_cpu_stall_panicking)
 		return;
-	delta = jiffies - rsp->jiffies_stall;
+	delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
 	rnp = rdp->mynode;
-	if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
+	if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
 
 		/* We haven't checked in, so go dump stack. */
 		print_cpu_stall(rsp);
-- 
1.6.0.4

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