Preparatory patch for a lockless empty check of the hash bucket plist in futex_wake().
No functional change. Signed-off-by: Thomas Gleixner <[email protected]> --- kernel/futex.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) Index: linux-2.6/kernel/futex.c =================================================================== --- linux-2.6.orig/kernel/futex.c +++ linux-2.6/kernel/futex.c @@ -1548,15 +1548,14 @@ static inline void queue_unlock(struct f * @q: The futex_q to enqueue * @hb: The destination hash bucket * - * The hb->lock must be held by the caller, and is released here. A call to - * queue_me() is typically paired with exactly one call to unqueue_me(). The - * exceptions involve the PI related operations, which may use unqueue_me_pi() - * or nothing if the unqueue is done as part of the wake process and the unqueue - * state is implicit in the state of woken task (see futex_wait_requeue_pi() for - * an example). + * The hb->lock must be held by the caller. A call to queue_me() is + * typically paired with exactly one call to unqueue_me(). The + * exceptions involve the PI related operations, which may use + * unqueue_me_pi() or nothing if the unqueue is done as part of the + * wake process and the unqueue state is implicit in the state of + * woken task (see futex_wait_requeue_pi() for an example). */ static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) - __releases(&hb->lock) { int prio; @@ -1573,7 +1572,6 @@ static inline void queue_me(struct futex plist_node_init(&q->list, prio); plist_add(&q->list, &hb->chain); q->task = current; - spin_unlock(&hb->lock); } /** @@ -1834,6 +1832,11 @@ static void futex_wait_queue_me(struct f */ set_current_state(TASK_INTERRUPTIBLE); queue_me(q, hb); + /* + * Unlock _AFTER_ we queued ourself. See the comment describing + * the futex ordering guarantees on top of this file. + */ + queue_unlock(hb); /* Arm the timer */ if (timeout) { @@ -2085,6 +2088,11 @@ retry_private: * Only actually queue now that the atomic ops are done: */ queue_me(&q, hb); + /* + * Unlock _AFTER_ we queued ourself. See the comment describing + * the futex ordering guarantees on top of this file. + */ + queue_unlock(hb); WARN_ON(!q.pi_state); /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
