linux-kernel - Re: [PATCH RFC 4/7] md/raid10: convert read/write to use bio_submit

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Message-ID: <def0970e-0bf7-4a6d-9b68-692b40aeecae@oracle.com>
Date: Tue, 2 Sep 2025 07:18:01 +0100
From: John Garry <john.g.garry@...cle.com>
To: Christoph Hellwig <hch@...radead.org>, anthony <antmbox@...ngman.org.uk>
Cc: Yu Kuai <yukuai1@...weicloud.com>, colyli@...nel.org, hare@...e.de,
        tieren@...as.com, axboe@...nel.dk, tj@...nel.org, josef@...icpanda.com,
        song@...nel.org, akpm@...ux-foundation.org, neil@...wn.name,
        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 4/7] md/raid10: convert read/write to use
 bio_submit_split()

On 27/08/2025 08:31, Christoph Hellwig wrote:
> On Tue, Aug 26, 2025 at 06:35:10PM +0100, anthony wrote:
>> On 26/08/2025 10:14, Yu Kuai wrote:
>>>> Umm, that's actually a red flag.  If a device guarantees atomic behavior
>>>> it can't just fail it.  So I think REQ_ATOMIC should be disallowed
>>>> for md raid with bad block tracking.
>>>>
>>>
>>> I agree that do not look good, however, John explained while adding this
>>> that user should retry and fallback without REQ_ATOMIC to make things
>>> work as usual.
>>
>> Whether a device promises atomic write is orthogonal to whether that write
>> succeeds - it could fail for a whole host of reasons, so why can't "this is
>> too big to be atomic" just be another reason for failing?
> 
> Too big to be atomic is a valid failure reason.  But the limit needs
> to be documented in the queue limits beforehand.
> 
> 

What exactly could need to be documented?

We just report -EIO in this case (when we try to write to a bad blocks 
region with REQ_ATOMIC). In general, for RWF_ATOMIC, we report -EINVAL 
for too large/small a size.

BTW, do we realistically expect atomic writes HW support and bad blocks 
ever to meet?

Thanks,
John