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rcu: Add memory barriers for NOCB leader wakeup

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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]>
Cc: <[email protected]> # 4.6.x
This commit is contained in:
Paul E. McKenney 2017-04-28 20:11:09 -07:00
commit 6b5fc3a133
1 changed files with 2 additions and 0 deletions
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2
kernel/rcu/tree_plugin.h
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@ -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)