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

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Date:   Tue, 9 May 2023 11:09:57 -0400
From:   Waiman Long <longman@...hat.com>
To:     Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Cc:     Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] locking/qspinlock: Fix state-transition changes in
 comments

On 5/9/23 03:29, Qiuxu Zhuo wrote:
> 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);
Acked-by: Waiman Long <longman@...hat.com>