The following commit has been merged into the locking/urgent branch of tip: Commit-ID: 249955e51c8136189b3c66f54e212981a1350a0f Gitweb: https://git.kernel.org/tip/249955e51c8136189b3c66f54e212981a1350a0f Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Thu, 02 Sep 2021 11:48:50 +02:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Thu, 02 Sep 2021 22:07:18 +02:00 futex: Clarify comment for requeue_pi_wake_futex() It's slightly confusing. Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20210902094414.618613025@xxxxxxxxxxxxx --- kernel/futex.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 04164d4..82cd270 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,
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