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

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Message-ID: <7edded3f-1075-4c14-9db9-a62adc0a4aa3@acm.org>
Date: Tue, 2 Sep 2025 18:12:20 -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, yi.zhang@...wei.com,
 yangerkun@...wei.com, johnny.chenyi@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC v3 14/15] block: fix disordered IO in the case
 recursive split

On 9/2/25 6:00 PM, Yu Kuai wrote:
> Hi,
> 
> 在 2025/09/03 1:20, Bart Van Assche 写道:
>> 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@....org/)
> 
> Do you mean we should remove the bdev_is_zoned() checking? I added this
> checking because I'm not quite sure about details in zone device, and
> this checking is aimed at prevent functional changes in zone device.

Yes, the bdev_is_zoned() check should be removed. I spent a significant
amount of time on root-causing and proposing fixes for write errors
caused by recursive bio splitting for zoned devices. What I learned by
analyzing these write errors is the basis for this feedback.

> So I don't think this change will cause write errors, the write errors
> should already exist before this set, right?

Agreed. Although I haven't checked this yet, if the bdev_is_zoned()
check is removed from this patch, this patch should fix the write errors
triggered by stacking a dm driver on top of a zoned block device if
inline encryption is enabled.

Thanks,

Bart.