diff options
| -rw-r--r-- | kernel/futex.c | 26 |
1 files changed, 20 insertions, 6 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index 04164d440d98..82cd270f25a0 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1954,12 +1954,26 @@ static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q) * @hb: the hash_bucket of the requeue target futex * * During futex_requeue, with requeue_pi=1, it is possible to acquire the - * target futex if it is uncontended or via a lock steal. Set the futex_q key - * to the requeue target futex so the waiter can detect the wakeup on the right - * futex, but remove it from the hb and NULL the rt_waiter so it can detect - * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock - * to protect access to the pi_state to fixup the owner later. Must be called - * with both q->lock_ptr and hb->lock held. + * target futex if it is uncontended or via a lock steal. + * + * 1) Set @q::key to the requeue target futex key so the waiter can detect + * the wakeup on the right futex. + * + * 2) Dequeue @q from the hash bucket. + * + * 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock + * acquisition. + * + * 4) Set the q->lock_ptr to the requeue target hb->lock for the case that + * the waiter has to fixup the pi state. + * + * 5) Complete the requeue state so the waiter can make progress. After + * this point the waiter task can return from the syscall immediately in + * case that the pi state does not have to be fixed up. + * + * 6) Wake the waiter task. + * + * Must be called with both q->lock_ptr and hb->lock held. */ static inline void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, |