linux-kernel - Re: [PATCH -next] raid10: fix leak of io accounting

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Date:   Thu, 9 Mar 2023 14:36:35 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     Yu Kuai <yukuai1@...weicloud.com>, song@...nel.org
Cc:     linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        yukuai3@...wei.com, yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH -next] raid10: fix leak of io accounting

Hi,

What do you mean 'leak' here?

On 3/4/23 15:01, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
>
> handle_read_error() will resumit r10_bio by raid10_read_request(), which
> will call bio_start_io_acct() again, while bio_end_io_acct() will only
> be called once.
>
> Fix the problem by don't account io again from handle_read_error().

My understanding is it caused inaccurate io stats for bio which had a read
error.

> Fixes: 528bc2cf2fcc ("md/raid10: enable io accounting")
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
>   drivers/md/raid10.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 6c66357f92f5..4f8edb6ea3e2 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -1173,7 +1173,7 @@ static bool regular_request_wait(struct mddev *mddev, struct r10conf *conf,
>   }
>   
>   static void raid10_read_request(struct mddev *mddev, struct bio *bio,
> -				struct r10bio *r10_bio)
> +				struct r10bio *r10_bio, bool handle_error)
>   {
>   	struct r10conf *conf = mddev->private;
>   	struct bio *read_bio;
> @@ -1244,7 +1244,7 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
>   	}
>   	slot = r10_bio->read_slot;
>   
> -	if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
> +	if (!handle_error && blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
>   		r10_bio->start_time = bio_start_io_acct(bio);

I think a simpler way is just check R10BIO_ReadError here.

Thanks,
Guoqing