[patch V3 57/64] futex: Restructure futex_requeue()

Thomas Gleixner
2021-08-05T15:45:57Z

From: Thomas Gleixner <tglx@linutronix.de>

No point in taking two more 'requeue_pi' conditionals just to get to the
requeue. Same for the requeue_pi case just the other way round.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/futex.c | 90 +++++++++++++++++++++++++--------------------------------
1 file changed, 41 insertions(+), 49 deletions(-)
---
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2119,20 +2119,17 @@ static int futex_requeue(u32 __user *uad
break;
}

- /*
- * Wake nr_wake waiters. For requeue_pi, if we acquired the
- * lock, we already woke the top_waiter. If not, it will be
- * woken by futex_unlock_pi().
- */
- if (++task_count <= nr_wake && !requeue_pi) {
- mark_wake_futex(&wake_q, this);
+ /* Plain futexes just wake or requeue and are done */
+ if (!requeue_pi) {
+ if (++task_count <= nr_wake)
+ mark_wake_futex(&wake_q, this);
+ else
+ requeue_futex(this, hb1, hb2, &key2);
continue;
}

/* Ensure we requeue to the expected futex for requeue_pi. */
- if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
- /* Don't account for it */
- task_count--;
+ if (!match_futex(this->requeue_pi_key, &key2)) {
ret = -EINVAL;
break;
}
@@ -2140,50 +2137,45 @@ static int futex_requeue(u32 __user *uad
/*
* Requeue nr_requeue waiters and possibly one more in the case
* of requeue_pi if we couldn't acquire the lock atomically.
+ *
+ * Prepare the waiter to take the rt_mutex. Take a refcount
+ * on the pi_state and store the pointer in the futex_q
+ * object of the waiter.
*/
- if (requeue_pi) {
+ get_pi_state(pi_state);
+ this->pi_state = pi_state;
+ ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
+ this->rt_waiter, this->task);
+ if (ret == 1) {
+ /*
+ * We got the lock. We do neither drop the refcount
+ * on pi_state nor clear this->pi_state because the
+ * waiter needs the pi_state for cleaning up the
+ * user space value. It will drop the refcount
+ * after doing so.
+ */
+ requeue_pi_wake_futex(this, &key2, hb2);
+ task_count++;
+ continue;
+ } else if (ret) {
+ /*
+ * rt_mutex_start_proxy_lock() detected a potential
+ * deadlock when we tried to queue that waiter.
+ * Drop the pi_state reference which we took above
+ * and remove the pointer to the state from the
+ * waiters futex_q object.
+ */
+ this->pi_state = NULL;
+ put_pi_state(pi_state);
/*
- * Prepare the waiter to take the rt_mutex. Take a
- * refcount on the pi_state and store the pointer in
- * the futex_q object of the waiter.
+ * We stop queueing more waiters and let user space
+ * deal with the mess.
*/
- get_pi_state(pi_state);
- this->pi_state = pi_state;
- ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
- this->rt_waiter,
- this->task);
- if (ret == 1) {
- /*
- * We got the lock. We do neither drop the
- * refcount on pi_state nor clear
- * this->pi_state because the waiter needs the
- * pi_state for cleaning up the user space
- * value. It will drop the refcount after
- * doing so.
- */
- requeue_pi_wake_futex(this, &key2, hb2);
- continue;
- } else if (ret) {
- /*
- * rt_mutex_start_proxy_lock() detected a
- * potential deadlock when we tried to queue
- * that waiter. Drop the pi_state reference
- * which we took above and remove the pointer
- * to the state from the waiters futex_q
- * object.
- */
- this->pi_state = NULL;
- put_pi_state(pi_state);
- /* Don't account for it */
- task_count--;
- /*
- * We stop queueing more waiters and let user
- * space deal with the mess.
- */
- break;
- }
+ break;
}
+ /* Waiter is queued, move it to hb2 */
requeue_futex(this, hb1, hb2, &key2);
+ task_count++;
}

/*