4.11-stable review patch. If anyone has any objections, please let me know.
------------------ From: Paul E. McKenney <[email protected]> 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 <[email protected]> Tested-by: Krister Johansen <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/rcu/tree_plugin.h | 2 ++ 1 file changed, 2 insertions(+) --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1769,6 +1769,7 @@ 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); } } @@ -2023,6 +2024,7 @@ 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)
