This is a note to let you know that I've just added the patch titled
rcu: Add memory barriers for NOCB leader wakeup
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rcu-add-memory-barriers-for-nocb-leader-wakeup.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 6b5fc3a1331810db407c9e0e673dc1837afdc9d0 Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Date: Fri, 28 Apr 2017 20:11:09 -0700
Subject: rcu: Add memory barriers for NOCB leader wakeup
From: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
commit 6b5fc3a1331810db407c9e0e673dc1837afdc9d0 upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree_plugin.h | 2 ++
1 file changed, 2 insertions(+)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1767,6 +1767,7 @@ static void wake_nocb_leader(struct rcu_
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);
}
}
@@ -2021,6 +2022,7 @@ 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)
Patches currently in stable-queue which might be from paulmck@xxxxxxxxxxxxxxxxxx are
queue-4.9/rcu-add-memory-barriers-for-nocb-leader-wakeup.patch