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Message-ID: <c617aa86-3b03-4e35-8c93-6d14d4e50398@redhat.com>
Date: Sun, 31 Dec 2023 23:08:07 -0500
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Subject: Re: [PATCH next v2 1/5] locking/osq_lock: Defer clearing node->locked
 until the slow osq_lock() path.
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To: David Laight <David.Laight@ACULAB.COM>,
 "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
 "'peterz@infradead.org'" <peterz@infradead.org>
Cc: "'mingo@redhat.com'" <mingo@redhat.com>,
 "'will@kernel.org'" <will@kernel.org>,
 "'boqun.feng@gmail.com'" <boqun.feng@gmail.com>,
 'Linus Torvalds' <torvalds@linux-foundation.org>,
 "'virtualization@lists.linux-foundation.org'"
 <virtualization@lists.linux-foundation.org>,
 'Zeng Heng' <zengheng4@huawei.com>
References: <2b4e8a5816a742d2bd23fdbaa8498e80@AcuMS.aculab.com>
 <714ca2e587cf4cd485ae04e5afb8d5bb@AcuMS.aculab.com>
From: Waiman Long <longman@redhat.com>
In-Reply-To: <714ca2e587cf4cd485ae04e5afb8d5bb@AcuMS.aculab.com>
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On 12/31/23 16:51, David Laight wrote:
> Since node->locked cannot be set before the assignment to prev->next
> it is save to clear it in the slow path.
>
> Signed-off-by: David Laight <david.laight@aculab.com>
> ---
>   kernel/locking/osq_lock.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
> index 75a6f6133866..e0bc74d85a76 100644
> --- a/kernel/locking/osq_lock.c
> +++ b/kernel/locking/osq_lock.c
> @@ -97,7 +97,6 @@ bool osq_lock(struct optimistic_spin_queue *lock)
>   	int curr = encode_cpu(smp_processor_id());
>   	int old;
>   
> -	node->locked = 0;
>   	node->next = NULL;
>   	node->cpu = curr;
>   
> @@ -111,6 +110,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
>   	if (old == OSQ_UNLOCKED_VAL)
>   		return true;
>   
> +	node->locked = 0;
>   	prev = decode_cpu(old);
>   	node->prev = prev;
>   

Reviewed-by: Waiman Long <longman@redhat.com>