linux-kernel - Re: [PATCH] block: fix disordered IO in the case recursive split

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Message-ID: <7db2eb2c-9566-4d6b-9f82-a0f65110a807@suse.de>
Date: Thu, 21 Aug 2025 11:33:59 +0200
From: Hannes Reinecke <hare@...e.de>
To: Christoph Hellwig <hch@...radead.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc: axboe@...nel.dk, neil@...wn.name, akpm@...ux-foundation.org,
 linux-block@...r.kernel.org, linux-raid@...r.kernel.org,
 linux-kernel@...r.kernel.org, colyli@...nel.org, xni@...hat.com,
 yi.zhang@...wei.com, yangerkun@...wei.com, johnny.chenyi@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] block: fix disordered IO in the case recursive split

On 8/21/25 11:02, Christoph Hellwig wrote:
> On Thu, Aug 21, 2025 at 04:56:33PM +0800, Yu Kuai wrote:
>> Can you give some examples as how to chain the right way?
> 
> fs/xfs/xfs_bio_io.c: xfs_rw_bdev
> fs/xfs/xfs_buf.c: xfs_buf_submit_bio
> fs/xfs/xfs_log.c: xlog_write_iclog
> 
>> BTW, for all
>> the io split case, should this order be fixed? I feel we should, this
>> disorder can happen on any stack case, where top max_sector is greater
>> than stacked disk.
> 
> Yes, I've been trying get Bart to fix this for a while instead of
> putting in a workaround very similar to the one proposed here,
> but so far nothing happened.
> 
> 
This feels like a really stupid fix, but wouldn't that help?

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 023649fe2476..2b342bb59612 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5478,7 +5478,6 @@ static struct bio *chunk_aligned_read(struct mddev 
*mddev, struct bio *raid_bio)
                 split = bio_split(raid_bio, sectors, GFP_NOIO, 
&conf->bio_split);
                 bio_chain(split, raid_bio);
                 submit_bio_noacct(raid_bio);
-               raid_bio = split;
         }


Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich