linux-kernel - Re: [PATCH] locking/rwsem: use OWNER_NONSPINNABLE directly instead of OWNER

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Message-ID: <7a006014-bf6e-4480-bd61-b0333c74e3a4@redhat.com>
Date: Fri, 13 Jun 2025 01:52:43 -0400
From: Waiman Long <llong@...hat.com>
To: alexjlzheng@...il.com, peterz@...radead.org, will@...nel.org,
 boqun.feng@...il.com
Cc: linux-kernel@...r.kernel.org, Jinliang Zheng <alexjlzheng@...cent.com>
Subject: Re: [PATCH] locking/rwsem: use OWNER_NONSPINNABLE directly instead of
 OWNER_SPINNABLE


On 6/10/25 9:01 AM, alexjlzheng@...il.com wrote:
> From: Jinliang Zheng <alexjlzheng@...cent.com>
>
> After commit 7d43f1ce9dd0 ("locking/rwsem: Enable time-based spinning on
> reader-owned rwsem"), OWNER_SPINNABLE contains all possible values except
> OWNER_NONSPINNABLE, namely OWNER_NULL | OWNER_WRITER | OWNER_READER.
>
> Therefore, it is better to use OWNER_NONSPINNABLE directly to determine
> whether to exit optimistic spin.
>
> And, remove useless OWNER_SPINNABLE to simplify the code.
>
> Signed-off-by: Jinliang Zheng <alexjlzheng@...cent.com>
> ---
>   kernel/locking/rwsem.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index 2ddb827e3bea..8572dba95af4 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -727,8 +727,6 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
>   	return ret;
>   }
>   
> -#define OWNER_SPINNABLE		(OWNER_NULL | OWNER_WRITER | OWNER_READER)
> -
>   static inline enum owner_state
>   rwsem_owner_state(struct task_struct *owner, unsigned long flags)
>   {
> @@ -835,7 +833,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
>   		enum owner_state owner_state;
>   
>   		owner_state = rwsem_spin_on_owner(sem);
> -		if (!(owner_state & OWNER_SPINNABLE))
> +		if (owner_state == OWNER_NONSPINNABLE)
>   			break;
>   
>   		/*

Right, OWNER_SPINNABLE is no longer needed after commit 7d43f1ce9dd0.

Acked-by: Waiman Long <longman@...hat.com>