From 249955e51c8136189b3c66f54e212981a1350a0f Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 2 Sep 2021 11:48:50 +0200
Subject: [PATCH] futex: Clarify comment for requeue_pi_wake_futex()
Git-commit: 249955e51c8136189b3c66f54e212981a1350a0f
Patch-mainline: v5.15-rc1
References: bsc#1190137 bsc#1189998

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
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>

---
 kernel/futex.c | 26 ++++++++++++++++++++------
 1 file 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,
-- 
2.26.2