Re: [PATCH v2 2/3] md/raid1,raid10: fix error-path detection with md_cloned_bio()

[Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>]

On Fri, May 22, 2026 at 12:23 +0800, Yu Kuai wrote:
> Hi,
>
> 在 2026/5/21 17:14, Abd-Alrhman Masalkhi 写道:
>> The original bio resubmitted via bio_list is not executing in the raid1d
>> thread context, so blocking on is_suspended() is correct and will not
>> cause a deadlock. The suspension deadlock risk only exists for
>> md_cloned_bio executing in the raid1d thread context in the error path.
>> And in this case it is always true that if we are executing in the
>> raid1d thread context the bio will already be a md_cloned_bio on entry
>> to md_handle_request(), even if current->bio_list was set, because (and as
>> @Xiao has mentioned) every time we split a bio in the error path we are
>> resubmitting the md_cloned_bio remainder, never the original bio.
>
> I do understand this, if original bio or resubmitted bio only split at
> raid1_read_request, there is no problem. What I feel is not safe is that
> bio can split somewhere else.
>
> This is possible for raid5, However, take a closer look at raid1/10, I
> feel it's not possible for resubmitted io to split in bio_split_to_limits.
> Even if it happens, it's probably someone else to blame.
>

Agreed. Since bio_split_to_limits() has been mentioned, I am wondering
whether a resubmitted md_cloned_bio could end up being split there for
raid456. I have not looked into the raid456 code yet; after finishing
raid1 and raid10, I will move on to the others.
I am considering skipping the redundant call to bio_split_to_limits()
when md_cloned_bio() is true. However, I am not sure whether this would
be safe for raid456.

> -- 
> Thansk,
> Kuai

-- 
Best Regards,
Abd-Alrhman