linux-kernel - Re: [PATCH RFC v3 07/15] md/raid1: convert to use bio_submit_split

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Message-ID: <4c823b51-f623-9a65-6d38-cfa874857eb2@huaweicloud.com>
Date: Mon, 1 Sep 2025 16:03:22 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Damien Le Moal <dlemoal@...nel.org>, Yu Kuai <yukuai1@...weicloud.com>,
 hch@...radead.org, colyli@...nel.org, hare@...e.de, tieren@...as.com,
 axboe@...nel.dk, tj@...nel.org, josef@...icpanda.com, song@...nel.org,
 kmo@...erainc.com, satyat@...gle.com, ebiggers@...gle.com, neil@...wn.name,
 akpm@...ux-foundation.org
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, linux-raid@...r.kernel.org, yi.zhang@...wei.com,
 yangerkun@...wei.com, johnny.chenyi@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC v3 07/15] md/raid1: convert to use
 bio_submit_split_bioset()

Hi,

在 2025/09/01 14:43, Damien Le Moal 写道:
> On 9/1/25 12:32 PM, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> Unify bio split code, and prepare to fix disordered split IO.
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> 
> [...]
> 
>> @@ -1586,18 +1577,13 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
>>   		max_sectors = min_t(int, max_sectors,
>>   				    BIO_MAX_VECS * (PAGE_SIZE >> 9));
>>   	if (max_sectors < bio_sectors(bio)) {
>> -		struct bio *split = bio_split(bio, max_sectors,
>> -					      GFP_NOIO, &conf->bio_split);
>> -
>> -		if (IS_ERR(split)) {
>> -			error = PTR_ERR(split);
>> +		bio = bio_submit_split_bioset(bio, max_sectors,
>> +					      &conf->bio_split);
>> +		if (!bio) {
>> +			set_bit(R1BIO_Returned, &r1_bio->state);
> 
> Before it was "set_bit(R1BIO_Uptodate, &r1_bio->state);" that was done. Now it
> is R1BIO_Returned that is set. The commit message does not mention this change
> at all. Is this a bug fix ? If yes, that should be in a pre patch before the
> conversion to using bio_submit_split_bioset().

There should be no functional changes, before the change we:

1) set bio->bi_status to split error value;
2) set R1BIO_Uptodate;
3) raid_end_bio_io() check R1BIO_Returned is not set, and call
call_bio_endio();
4) call_bio_endio() check R1BIO_Uptodate is already set, keep the
bio->bi_status that is by split error;

With this change:
1) bio_submit_split_bioset() already fail the bio will split error;
2) set R1BIO_Returned;
3) raid_end_bio_io() check R1BIO_Returned is set and do nothing with the
bio;

And the same with raid10 in patch 8,9;

Perhaps I'll emphasize there is no function changes and explain a bit.

Thanks,
Kuai
> 
>>   			goto err_handle;
>>   		}
>>   
>> -		bio_chain(split, bio);
>> -		trace_block_split(split, bio->bi_iter.bi_sector);
>> -		submit_bio_noacct(bio);
>> -		bio = split;
>>   		r1_bio->master_bio = bio;
>>   		r1_bio->sectors = max_sectors;
>>   	}
>> @@ -1687,8 +1673,6 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
>>   		}
>>   	}
>>   
>> -	bio->bi_status = errno_to_blk_status(error);
>> -	set_bit(R1BIO_Uptodate, &r1_bio->state);
>>   	raid_end_bio_io(r1_bio);
>>   }
> 
>