linux-kernel - Re: [PATCH RFC 0/6] bio_split() error handling rework

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Message-ID: <bbe71976-c16c-4e3c-b110-6bf8eb709d54@suse.de>
Date: Mon, 23 Sep 2024 07:53:33 +0200
From: Hannes Reinecke <hare@...e.de>
To: John Garry <john.g.garry@...cle.com>, axboe@...nel.dk, hch@....de
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-raid@...r.kernel.org, martin.petersen@...cle.com
Subject: Re: [PATCH RFC 0/6] bio_split() error handling rework

On 9/19/24 11:22, John Garry wrote:
> bio_split() error handling could be improved as follows:
> - Instead of returning NULL for an error - which is vague - return a
>    PTR_ERR, which may hint what went wrong.
> - Remove BUG_ON() calls - which are generally not preferred - and instead
>    WARN and pass an error code back to the caller. Many callers of
>    bio_split() don't check the return code. As such, for an error we would
>    be getting a crash still from an invalid pointer dereference.
> 
> Most bio_split() callers don't check the return value. However, it could
> be argued the bio_split() calls should not fail. So far I have just
> fixed up the md RAID code to handle these errors, as that is my interest
> now.
> 
> Sending as an RFC as unsure if this is the right direction.
> 
> The motivator for this series was initial md RAID atomic write support in
> https://lore.kernel.org/linux-block/21f19b4b-4b83-4ca2-a93b-0a433741fd26@oracle.com/
> 
> There I wanted to ensure that we don't split an atomic write bio, and it
> made more sense to handle this in bio_split() (instead of the bio_split()
> caller).
> 
> John Garry (6):
>    block: Rework bio_split() return value
>    block: Error an attempt to split an atomic write in bio_split()
>    block: Handle bio_split() errors in bio_submit_split()
>    md/raid0: Handle bio_split() errors
>    md/raid1: Handle bio_split() errors
>    md/raid10: Handle bio_split() errors
> 
>   block/bio.c                 | 14 ++++++++++----
>   block/blk-crypto-fallback.c |  2 +-
>   block/blk-merge.c           |  5 +++++
>   drivers/md/raid0.c          | 10 ++++++++++
>   drivers/md/raid1.c          |  8 ++++++++
>   drivers/md/raid10.c         | 18 ++++++++++++++++++
>   6 files changed, 52 insertions(+), 5 deletions(-)
> 
You are missing '__bio_split_to_limits()' which looks as it would need 
to be modified, too.

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