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

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Message-ID: <66e481e6-ed2c-2ac2-bdd0-9e20a0ec9771@huaweicloud.com>
Date:   Thu, 9 Mar 2023 15:45:25 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Guoqing Jiang <guoqing.jiang@...ux.dev>,
        Yu Kuai <yukuai1@...weicloud.com>, song@...nel.org
Cc:     linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next] raid10: fix leak of io accounting

Hi,

在 2023/03/09 15:27, Guoqing Jiang 写道:
> 
> 
> On 3/9/23 14:56, Yu Kuai wrote:
>> Hi,
>>
>> 在 2023/03/09 14:36, Guoqing Jiang 写道:
>>> Hi,
>>>
>>> What do you mean 'leak' here?
>>
>> I try to mean that inflight counting is leaked, because it's increased
>> twice for one io.
> 
> How about change the subject to something like?
> 
> 'md/raid10: Don't call bio_start_io_acct twice for bio which experienced 
> read error'
> 
Of course, I'll change that in v2.

>>
>>>
>>> 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.
>>
>> No, I'm afraid this is incorrect because handle_read_error clears the
>> state before resubmiting the r10bio.
> 
> Right,
> 
> Acked-by: Guoqing Jiang <guoqing.jiang@...ux.dev>

Thanks for the review.
Kuai
> 
> Thanks,
> Guoqing
> .
>