summaryrefslogtreecommitdiff
path: root/kernel/futex.c
diff options
context:
space:
mode:
Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c80
1 files changed, 63 insertions, 17 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 067702335762..97e3f0f16553 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1422,6 +1422,16 @@ retry_private:
requeue_pi_wake_futex(this, &key2, hb2);
drop_count++;
continue;
+ } else if (ret == -EAGAIN) {
+ /*
+ * Waiter was woken by timeout or
+ * signal and has set pi_blocked_on to
+ * PI_WAKEUP_INPROGRESS before we
+ * tried to enqueue it on the rtmutex.
+ */
+ this->pi_state = NULL;
+ free_pi_state(pi_state);
+ continue;
} else if (ret) {
/* -EDEADLK */
this->pi_state = NULL;
@@ -2266,7 +2276,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
struct hrtimer_sleeper timeout, *to = NULL;
struct rt_mutex_waiter rt_waiter;
struct rt_mutex *pi_mutex = NULL;
- struct futex_hash_bucket *hb;
+ struct futex_hash_bucket *hb, *hb2;
union futex_key key2 = FUTEX_KEY_INIT;
struct futex_q q = futex_q_init;
int res, ret;
@@ -2288,8 +2298,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
* The waiter is allocated on our stack, manipulated by the requeue
* code while we sleep on uaddr.
*/
- debug_rt_mutex_init_waiter(&rt_waiter);
- rt_waiter.task = NULL;
+ rt_mutex_init_waiter(&rt_waiter, false);
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
if (unlikely(ret != 0))
@@ -2310,20 +2319,55 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
/* Queue the futex_q, drop the hb lock, wait for wakeup. */
futex_wait_queue_me(hb, &q, to);
- spin_lock(&hb->lock);
- ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
- spin_unlock(&hb->lock);
- if (ret)
- goto out_put_keys;
+ /*
+ * On RT we must avoid races with requeue and trying to block
+ * on two mutexes (hb->lock and uaddr2's rtmutex) by
+ * serializing access to pi_blocked_on with pi_lock.
+ */
+ raw_spin_lock_irq(&current->pi_lock);
+ if (current->pi_blocked_on) {
+ /*
+ * We have been requeued or are in the process of
+ * being requeued.
+ */
+ raw_spin_unlock_irq(&current->pi_lock);
+ } else {
+ /*
+ * Setting pi_blocked_on to PI_WAKEUP_INPROGRESS
+ * prevents a concurrent requeue from moving us to the
+ * uaddr2 rtmutex. After that we can safely acquire
+ * (and possibly block on) hb->lock.
+ */
+ current->pi_blocked_on = PI_WAKEUP_INPROGRESS;
+ raw_spin_unlock_irq(&current->pi_lock);
+
+ spin_lock(&hb->lock);
+
+ /*
+ * Clean up pi_blocked_on. We might leak it otherwise
+ * when we succeeded with the hb->lock in the fast
+ * path.
+ */
+ raw_spin_lock_irq(&current->pi_lock);
+ current->pi_blocked_on = NULL;
+ raw_spin_unlock_irq(&current->pi_lock);
+
+ ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
+ spin_unlock(&hb->lock);
+ if (ret)
+ goto out_put_keys;
+ }
/*
- * In order for us to be here, we know our q.key == key2, and since
- * we took the hb->lock above, we also know that futex_requeue() has
- * completed and we no longer have to concern ourselves with a wakeup
- * race with the atomic proxy lock acquisition by the requeue code. The
- * futex_requeue dropped our key1 reference and incremented our key2
- * reference count.
+ * In order to be here, we have either been requeued, are in
+ * the process of being requeued, or requeue successfully
+ * acquired uaddr2 on our behalf. If pi_blocked_on was
+ * non-null above, we may be racing with a requeue. Do not
+ * rely on q->lock_ptr to be hb2->lock until after blocking on
+ * hb->lock or hb2->lock. The futex_requeue dropped our key1
+ * reference and incremented our key2 reference count.
*/
+ hb2 = hash_futex(&key2);
/* Check if the requeue code acquired the second futex for us. */
if (!q.rt_waiter) {
@@ -2332,9 +2376,10 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
* did a lock-steal - fix up the PI-state in that case.
*/
if (q.pi_state && (q.pi_state->owner != current)) {
- spin_lock(q.lock_ptr);
+ spin_lock(&hb2->lock);
+ BUG_ON(&hb2->lock != q.lock_ptr);
ret = fixup_pi_state_owner(uaddr2, &q, current);
- spin_unlock(q.lock_ptr);
+ spin_unlock(&hb2->lock);
}
} else {
/*
@@ -2347,7 +2392,8 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
debug_rt_mutex_free_waiter(&rt_waiter);
- spin_lock(q.lock_ptr);
+ spin_lock(&hb2->lock);
+ BUG_ON(&hb2->lock != q.lock_ptr);
/*
* Fixup the pi_state owner and possibly acquire the lock if we
* haven't already.