linux-kernel - Re: [PATCH v2] locking/rtmutex: Fix incorrect spinning condition

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Date:   Sun, 19 Dec 2021 16:09:20 -0500
From:   Waiman Long <longman@...hat.com>
To:     Zqiang <qiang1.zhang@...el.com>, peterz@...radead.org,
        mingo@...hat.com, will@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] locking/rtmutex: Fix incorrect spinning condition

On 12/17/21 02:42, Zqiang wrote:
> When the lock owner is on CPU and not need resched, the current waiter
> need to be checked, if it not longer top the waiter, stop spinning.

Incorrect grammar, should be "if it is no longer the top waiter". There 
is a similar typo in the existing code comment too.

You can modify the subject line to [PATCH-tip ...] to indicate that it 
is supposed to be apply on top of the tip tree. Other than that, the 
patch looks good.

Cheers,
Longman

>
> Fixes: c3123c431447 ("locking/rtmutex: Dont dereference waiter lockless")
> Signed-off-by: Zqiang <qiang1.zhang@...el.com>
> ---
>   v1->v2:
>   Modify description information.
>
>   kernel/locking/rtmutex.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 0c1f2e3f019a..8555c4efe97c 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -1383,7 +1383,7 @@ static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
>   		 *  - the VCPU on which owner runs is preempted
>   		 */
>   		if (!owner_on_cpu(owner) || need_resched() ||
> -		    rt_mutex_waiter_is_top_waiter(lock, waiter)) {
> +		    !rt_mutex_waiter_is_top_waiter(lock, waiter)) {
>   			res = false;
>   			break;
>   		}