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Message-ID: <84e5f6d5-3217-e1cf-6a3f-c337a6737e5d@redhat.com>
Date:   Wed, 12 Apr 2023 08:10:58 -0400
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Subject: Re: [PATCH v2] locking/rwsem: Add __always_inline annotation to
 __down_read_common()
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To:     John Stultz <jstultz@google.com>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     Minchan Kim <minchan@kernel.org>,
        Tim Murray <timmurray@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>, kernel-team@android.com,
        stable@vger.kernel.org
References: <20230412023839.2869114-1-jstultz@google.com>
 <20230412035905.3184199-1-jstultz@google.com>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <20230412035905.3184199-1-jstultz@google.com>
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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@kernel.org>
> Cc: Tim Murray <timmurray@google.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: kernel-team@android.com
> Cc: stable@vger.kernel.org
> Fixes: c995e638ccbb ("locking/rwsem: Fold __down_{read,write}*()")
> Reported-by: Tim Murray <timmurray@google.com>
> Signed-off-by: John Stultz <jstultz@google.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@redhat.com>