Commit c5e9bfe6 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Greg Kroah-Hartman

rcu: Add memory barriers for NOCB leader wakeup

commit 6b5fc3a1 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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarKrister Johansen <kjlx@templeofstupid.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 101cbdea
...@@ -1769,6 +1769,7 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force) ...@@ -1769,6 +1769,7 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) { if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) {
/* Prior smp_mb__after_atomic() orders against prior enqueue. */ /* Prior smp_mb__after_atomic() orders against prior enqueue. */
WRITE_ONCE(rdp_leader->nocb_leader_sleep, false); WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
smp_mb(); /* ->nocb_leader_sleep before swake_up(). */
swake_up(&rdp_leader->nocb_wq); swake_up(&rdp_leader->nocb_wq);
} }
} }
...@@ -2023,6 +2024,7 @@ static void nocb_leader_wait(struct rcu_data *my_rdp) ...@@ -2023,6 +2024,7 @@ static void nocb_leader_wait(struct rcu_data *my_rdp)
* nocb_gp_head, where they await a grace period. * nocb_gp_head, where they await a grace period.
*/ */
gotcbs = false; gotcbs = false;
smp_mb(); /* wakeup before ->nocb_head reads. */
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head); rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
if (!rdp->nocb_gp_head) if (!rdp->nocb_gp_head)
......
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