Commit-ID: 6b5fc3a1331810db407c9e0e673dc1837afdc9d0
Gitweb: http://git.kernel.org/tip/6b5fc3a1331810db407c9e0e673dc1837afdc9d0
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Fri, 28 Apr 2017 20:11:09 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Thu, 8 Jun 2017 18:51:59 -0700
rcu: Add memory barriers for NOCB leader wakeup
Wait/wakeup operations do not guarantee ordering on their own. Instead,
either locking or memory barriers are required. This commit therefore
adds memory barriers to wake_nocb_leader() and nocb_leader_wait().
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Tested-by: Krister Johansen <kjlx@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.6.x
---
kernel/rcu/tree_plugin.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0b10425..573fbe9 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1810,6 +1810,7 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) {
/* Prior smp_mb__after_atomic() orders against prior enqueue. */
WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
+ smp_mb(); /* ->nocb_leader_sleep before swake_up(). */
swake_up(&rdp_leader->nocb_wq);
}
}
@@ -2064,6 +2065,7 @@ wait_again:
* nocb_gp_head, where they await a grace period.
*/
gotcbs = false;
+ smp_mb(); /* wakeup before ->nocb_head reads. */
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
if (!rdp->nocb_gp_head)
--
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