Re: [PATCH 6.6 005/568] md: fix deadlock between mddev_suspend and flush bio

[Andrew Kanner <andrew.kanner@gmail.com>]

> [...]
>
> Additionally, the only difference between fixing the issue and before is
> that there is no return error handling of make_request(). But after
> previous patch cleaned md_write_start(), make_requst() only return error
> in raid5_make_request() by dm-raid, see commit 41425f96d7aa ("dm-raid456,
> md/raid456: fix a deadlock for dm-raid456 while io concurrent with
> reshape)". Since dm always splits data and flush operation into two
> separate io, io size of flush submitted by dm always is 0, make_request()
> will not be called in md_submit_flush_data(). To prevent future
> modifications from introducing issues, add WARN_ON to ensure
> make_request() no error is returned in this context.
>
> [...]
> @@ -560,8 +552,20 @@ static void md_submit_flush_data(struct work_struct *ws)
>  		bio_endio(bio);
>  	} else {
>  		bio->bi_opf &= ~REQ_PREFLUSH;
> -		md_handle_request(mddev, bio);
> +
> +		/*
> +		 * make_requst() will never return error here, it only
> +		 * returns error in raid5_make_request() by dm-raid.
> +		 * Since dm always splits data and flush operation into
> +		 * two separate io, io size of flush submitted by dm
> +		 * always is 0, make_request() will not be called here.
> +		 */
> +		if (WARN_ON_ONCE(!mddev->pers->make_request(mddev, bio)))
> +			bio_io_error(bio);;
>  	}

Hello,

It looks we can hit this WARN_ON_ONCE() after which rootfs is
switching to read-only:

May 20 15:13:35 hostname kernel: WARNING: CPU: 35 PID: 1517323 at drivers/md/md.c:621 md_submit_flush_data+0x9b/0xe0
...
May 20 15:13:35 hostname kernel: XFS (md125): log I/O error -5
May 20 15:13:35 hostname kernel: XFS (md125): Filesystem has been shut down due to log error (0x2).
May 20 15:13:35 hostname kernel: XFS (md125): Please unmount the filesystem and rectify the problem(s).

Can you double check if the following regression is actual?

Since both stable/linux-6.1.y and stable/linux-6.6.y branches don't
have b75197e86e6d ("md: Remove flush handling") there is a minor issue
with this backport.

Statement "previous patch cleaned md_write_start(), make_requst() only
return error in raid5_make_request() by dm-raid" will not work for
both branches since 03e792eaf18e ("md: change the return value type of
md_write_start to void") was not backported.

So we should either backport it, or do error handling, not the
WARN_ON_ONCE().

-- 
Andrew Kanner