rcu: Flag lockless access to ->gp_flags with ACCESS_ONCE()

This commit applies ACCESS_ONCE() to an outside-of-lock access to
->gp_flags.  Although it is hard to imagine any sane compiler messing
this particular case up, the documentation benefits are substantial.
Plus the definition of "sane compiler" grows ever looser.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 62b67b7..6d028fd 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1481,7 +1481,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
                /* Handle grace-period start. */
                for (;;) {
                        wait_event_interruptible(rsp->gp_wq,
-                                                rsp->gp_flags &
+                                                ACCESS_ONCE(rsp->gp_flags) &
                                                 RCU_GP_FLAG_INIT);
                        if (rcu_gp_init(rsp))
                                break;