diff options
| -rw-r--r-- | kernel/locking/qspinlock_paravirt.h | 23 |
1 files changed, 18 insertions, 5 deletions
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index 489a87884337..ab8b1bb8caa4 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -244,13 +244,17 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node) if (!lp) { /* ONCE */ lp = pv_hash(lock, pn); /* - * lp must be set before setting _Q_SLOW_VAL + * We must hash before setting _Q_SLOW_VAL, such that + * when we observe _Q_SLOW_VAL in __pv_queued_spin_unlock() + * we'll be sure to be able to observe our hash entry. * - * [S] lp = lock [RmW] l = l->locked = 0 - * MB MB - * [S] l->locked = _Q_SLOW_VAL [L] lp + * [S] pn->state + * [S] <hash> [Rmw] l->locked == _Q_SLOW_VAL + * MB RMB + * [RmW] l->locked = _Q_SLOW_VAL [L] <unhash> + * [L] pn->state * - * Matches the cmpxchg() in __pv_queued_spin_unlock(). + * Matches the smp_rmb() in __pv_queued_spin_unlock(). */ if (!cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL)) { /* @@ -306,6 +310,15 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock) } /* + * A failed cmpxchg doesn't provide any memory-ordering guarantees, + * so we need a barrier to order the read of the node data in + * pv_unhash *after* we've read the lock being _Q_SLOW_VAL. + * + * Matches the cmpxchg() in pv_wait_head() setting _Q_SLOW_VAL. + */ + smp_rmb(); + + /* * Since the above failed to release, this must be the SLOW path. * Therefore start by looking up the blocked node and unhashing it. */ |