From 4ee0a603926cad973e4d384f48c5e279a0fd4118 Mon Sep 17 00:00:00 2001 From: Dongdong Deng Date: Tue, 28 Sep 2010 16:32:43 +0800 Subject: [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. Although use without ACCESS_ONCE() is safe due to the value loaded being used but once, the ACCESS_ONCE() is a good documentation aid -- the variables are being loaded without the services of a lock. Signed-off-by: Dongdong Deng CC: Dipankar Sarma CC: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e750735..ccdc04c 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -545,9 +545,9 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) if (rcu_cpu_stall_suppress) 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); -- 2.7.4