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Subject: Re: [PATCH 2/3] md/raid10: factor out get_rdev_repl_from_mirror()
To:     linan666@huaweicloud.com, song@kernel.org,
        guoqing.jiang@cloud.ionos.com, colyli@suse.de, xni@redhat.com
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        linan122@huawei.com, yi.zhang@huawei.com, houtao1@huawei.com,
        yangerkun@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20230628015752.102267-1-linan666@huaweicloud.com>
 <20230628015752.102267-3-linan666@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <36a6be92-f9c5-fd7c-20d9-741e2a6f133f@huaweicloud.com>
Date:   Wed, 28 Jun 2023 17:26:38 +0800
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Hi,

?? 2023/06/28 9:57, linan666@huaweicloud.com д??:
> From: Li Nan <linan122@huawei.com>
> 
> Factor out a helper to get 'rdev' and 'replacement' from config->mirrors.
> Just to make code cleaner and prepare to fix the bug of io loss while
> 'replacement' replace 'rdev'.
> 
> There is no functional change.
> 
> Signed-off-by: Li Nan <linan122@huawei.com>
> ---
>   drivers/md/raid10.c | 30 +++++++++++++++++++++---------
>   1 file changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 3e6a09aaaba6..eaaf6307ddda 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -1346,6 +1346,26 @@ static void raid10_write_one_disk(struct mddev *mddev, struct r10bio *r10_bio,
>   	}
>   }
>   
> +static void get_rdev_repl_from_mirror(struct raid10_info *mirror,
> +				 struct md_rdev **prdev,
> +				 struct md_rdev **prrdev)

I don't like this name, but I can live with this for now, related code
will be removed eventually.

Reviewed-by: Yu Kuai <yukuai3@huawei.com>
> +{
> +	struct md_rdev *rdev, *rrdev;
> +
> +	rrdev = rcu_dereference(mirror->replacement);
> +	/*
> +	 * Read replacement first to prevent reading both rdev and
> +	 * replacement as NULL during replacement replace rdev.
> +	 */
> +	smp_mb();
> +	rdev = rcu_dereference(mirror->rdev);
> +	if (rdev == rrdev)
> +		rrdev = NULL;
> +
> +	*prrdev = rrdev;
> +	*prdev = rdev;
> +}
> +
>   static void wait_blocked_dev(struct mddev *mddev, struct r10bio *r10_bio)
>   {
>   	int i;
> @@ -1489,15 +1509,7 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
>   		int d = r10_bio->devs[i].devnum;
>   		struct md_rdev *rdev, *rrdev;
>   
> -		rrdev = rcu_dereference(conf->mirrors[d].replacement);
> -		/*
> -		 * Read replacement first to prevent reading both rdev and
> -		 * replacement as NULL during replacement replace rdev.
> -		 */
> -		smp_mb();
> -		rdev = rcu_dereference(conf->mirrors[d].rdev);
> -		if (rdev == rrdev)
> -			rrdev = NULL;
> +		get_rdev_repl_from_mirror(&conf->mirrors[d], &rdev, &rrdev);
>   		if (rdev && (test_bit(Faulty, &rdev->flags)))
>   			rdev = NULL;
>   		if (rrdev && (test_bit(Faulty, &rrdev->flags)))
>