linux-kernel - Re: [PATCH RFC v3 14/15] block: fix disordered IO in the case recursive split

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Message-ID: <e40b076d-583d-406b-b223-005910a9f46f@acm.org>
Date: Tue, 2 Sep 2025 10:20:01 -0700
From: Bart Van Assche <bvanassche@....org>
To: Yu Kuai <yukuai1@...weicloud.com>, hch@...radead.org, colyli@...nel.org,
 hare@...e.de, dlemoal@...nel.org, 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, yukuai3@...wei.com,
 yi.zhang@...wei.com, yangerkun@...wei.com, johnny.chenyi@...wei.com
Subject: Re: [PATCH RFC v3 14/15] block: fix disordered IO in the case
 recursive split

On 8/31/25 8:32 PM, Yu Kuai wrote:
> -void submit_bio_noacct_nocheck(struct bio *bio)
> +void submit_bio_noacct_nocheck(struct bio *bio, bool split)
>   {
>   	blk_cgroup_bio_start(bio);
>   	blkcg_bio_issue_init(bio);
> @@ -745,12 +745,16 @@ void submit_bio_noacct_nocheck(struct bio *bio)
>   	 * to collect a list of requests submited by a ->submit_bio method while
>   	 * it is active, and then process them after it returned.
>   	 */
> -	if (current->bio_list)
> -		bio_list_add(&current->bio_list[0], bio);
> -	else if (!bdev_test_flag(bio->bi_bdev, BD_HAS_SUBMIT_BIO))
> +	if (current->bio_list) {
> +		if (split && !bdev_is_zoned(bio->bi_bdev))
> +			bio_list_add_head(&current->bio_list[0], bio);
> +		else
> +			bio_list_add(&current->bio_list[0], bio);

The above change will cause write errors for zoned block devices. As I
have shown before, also for zoned block devices, if a bio is split
insertion must happen at the head of the list. See e.g.
"Re: [PATCH 1/2] block: Make __submit_bio_noacct() preserve the bio 
submission order"
(https://lore.kernel.org/linux-block/a0c89df8-4b33-409c-ba43-f9543fb1b091@acm.org/)

Thanks,

Bart.