Re: [PATCH] md: dont warn about sb update on auto read only arrays

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found no new issues
in this patch, but noticed 1 related pre-existing issue it does not
introduce:
- [Critical] md: badblocks log overlap check fails in
  super_1_allow_new_offset() [1]
--

commit 86c28dfbafd4341535246399e368c7eda6a1eb2d
Author: incharilla <incharilla@incharilla.site>

md: dont warn about sb update on auto read only arrays

This commit suppresses the read-only superblock update error message in
md_update_sb() when the array is in MD_AUTO_READ state.

> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 03e35386a8028..a0fc602899053 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -2819,7 +2819,8 @@ void md_update_sb(struct mddev *mddev, int force_change)
>  	if (!md_is_rdwr(mddev)) {
>  		if (force_change)
>  			set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);
> -		if (!mddev_is_dm(mddev))
> +		/* auto read only arrays write the sb once they become writable */
> +		if (!mddev_is_dm(mddev) && mddev->ro != MD_AUTO_READ)
>  			pr_err_ratelimited("%s: can't update sb for read-only array %s\n",
>  					   __func__, mdname(mddev));
>  		return;

[Severity: Critical]
This problem wasn't introduced by this patch, but does clearing
rdev->badblocks.size in md_update_sb() [1] cause
super_1_allow_new_offset() to miss badblocks log overlaps during a
reshape?

drivers/md/md.c:md_update_sb() {
	...
			if (rdev->badblocks.size) {
				md_write_metadata(mddev, rdev,
						  rdev->badblocks.sector,
						  rdev->badblocks.size << 9,
						  rdev->bb_page, 0);
				rdev->badblocks.size = 0;
			}
	...
}

drivers/md/md.c:super_1_allow_new_offset() {
	...
	if (rdev->badblocks.sector + rdev->badblocks.size > new_offset)
		return 0;

	return 1;
}

super_1_sync() sets rdev->badblocks.size, and md_update_sb() zeroes it as
soon as the badblocks metadata is written.  When a later reshape checks a
new data offset via super_1_allow_new_offset(), rdev->badblocks.size is 0,
allowing new_offset to overlap the on-disk badblocks log and corrupt
metadata or user data.

[1] https://sashiko.dev/#/bug/linux-18a3f5e9-47e5-4da7-8d4b-120745e50fdb

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261106-md-auto-read-only-sb-warn-v1-1-5bfde3559841@incharilla.site?part=1