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futex: Clarify comment for requeue_pi_wake_futex() 

It's slightly confusing.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210902094414.618613025@linutronix.de
This commit is contained in:
Thomas Gleixner 2021-09-02 11:48:50 +02:00
parent 4f07ec0d76
commit 249955e51c
1 changed files with 20 additions and 6 deletions
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26
kernel/futex.c
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@ -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,