linux-kernel - Re: [PATCH v2] locking/rwsem: Add __always_inline annotation to __down_read

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Date:   Wed, 12 Apr 2023 08:10:58 -0400
From:   Waiman Long <longman@...hat.com>
To:     John Stultz <jstultz@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Minchan Kim <minchan@...nel.org>,
        Tim Murray <timmurray@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>, kernel-team@...roid.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] locking/rwsem: Add __always_inline annotation to
 __down_read_common()

On 4/11/23 23:59, John Stultz wrote:
> Apparently despite it being marked inline, the compiler
> may not inline __down_read_common() which makes it difficult
> to identify the cause of lock contention, as the blocked
> function will always be listed as __down_read_common().
>
> So this patch adds __always_inline annotation to the
> function to force it to be inlines so the calling function
> will be listed.
>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Tim Murray <timmurray@...gle.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: kernel-team@...roid.com
> Cc: stable@...r.kernel.org
> Fixes: c995e638ccbb ("locking/rwsem: Fold __down_{read,write}*()")
> Reported-by: Tim Murray <timmurray@...gle.com>
> Signed-off-by: John Stultz <jstultz@...gle.com>
> ---
> v2: Reworked to use __always_inline instead of __sched as
>      suggested by Waiman Long
> ---
>   kernel/locking/rwsem.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index acb5a50309a1..e99eef8ea552 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -1240,7 +1240,7 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
>   /*
>    * lock for reading
>    */
> -static inline int __down_read_common(struct rw_semaphore *sem, int state)
> +static __always_inline int __down_read_common(struct rw_semaphore *sem, int state)
>   {
>   	int ret = 0;
>   	long count;
Reviewed-by: Waiman Long <longman@...hat.com>