linux-kernel - [PATCH v2 1/1] locking/qspinlock: Fix state-transition changes in comments

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Date:   Tue,  9 May 2023 15:29:02 +0800
From:   Qiuxu Zhuo <qiuxu.zhuo@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Cc:     Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
        Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/1] locking/qspinlock: Fix state-transition changes in comments

1. set_locked() only sets the locked field to 1 and doesn't touch
   the pending field. So the correct lock state transition is:

         *,*,0 -> *,*,1

2. The initial lock state when calling clear_pending_set_locked() is
   the state just after waiting for the locker goes away. So the
   state transition for clear_pending_set_locked() is:

         *,1,0 -> *,0,1

Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@...el.com>
---
 v1->v2:
 - Drop the state transition comments fixes (viewed from the current lock word value).
 - Update the commit message accordingly.

 kernel/locking/qspinlock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index ebe6b8ec7cb3..256021c87ac1 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -257,7 +257,7 @@ static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lo
  * set_locked - Set the lock bit and own the lock
  * @lock: Pointer to queued spinlock structure
  *
- * *,*,0 -> *,0,1
+ * *,*,0 -> *,*,1
  */
 static __always_inline void set_locked(struct qspinlock *lock)
 {
@@ -385,7 +385,7 @@ void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 	/*
 	 * take ownership and clear the pending bit.
 	 *
-	 * 0,1,0 -> 0,0,1
+	 * *,1,0 -> *,0,1
 	 */
 	clear_pending_set_locked(lock);
 	lockevent_inc(lock_pending);
-- 
2.17.1