Merge tag 'for-5.11/revert-problem-v5.10-raid-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm

Pull MD regression reverts from Mike Snitzer:
"A cascade of MD reverts occurred late in the v5.10-rcX cycle due to MD
raid10 discard optimizations having introduced potential for
corruption.

Those reverts exposed a dm-raid.c compiler warning that wasn't ever
knowingly introduced. That min_not_zero() type mismatch warning was
thought to be safely fixed simply by changing 'struct mddev' to use
'unsigned int' rather than int for chunk_sectors members in that
struct.

I proposed either using a cast local to dm-raid.c but thought changing
the type to 'unsigned int' more correct. While that may be, not enough
testing was paired with code review associated with making that
change. As such we were left exposed and the result was a report that
with v5.10 btrfs on MD RAID6 failed to mount:

https://lkml.org/lkml/2020/12/14/7

Given that report, it is justified to simply revert these offending
commits. stable@ has already taken steps to revert these for 5.10.1 -
this just makes sure mainline does so too"

* tag 'for-5.11/revert-problem-v5.10-raid-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
Revert "dm raid: fix discard limits for raid1 and raid10"
Revert "md: change mddev 'chunk_sectors' from int to unsigned"

drivers/md/dm-raid.c

···
 	blk_limits_io_opt(limits, chunk_size_bytes * mddev_data_stripes(rs));
 
 	/*
-	 * RAID10 personality requires bio splitting,
-	 * RAID0/1/4/5/6 don't and process large discard bios properly.
+	 * RAID1 and RAID10 personalities require bio splitting,
+	 * RAID0/4/5/6 don't and process large discard bios properly.
 	 */
-	if (rs_is_raid10(rs)) {
-		limits->discard_granularity = max(chunk_size_bytes,
-						  limits->discard_granularity);
-		limits->max_discard_sectors = min_not_zero(rs->md.chunk_sectors,
-							   limits->max_discard_sectors);
+	if (rs_is_raid1(rs) || rs_is_raid10(rs)) {
+		limits->discard_granularity = chunk_size_bytes;
+		limits->max_discard_sectors = rs->md.chunk_sectors;
 	}
 }
 

drivers/md/md.h

···
 	int				external;	/* metadata is
 							 * managed externally */
 	char				metadata_type[17]; /* externally set*/
-	unsigned int			chunk_sectors;
+	int				chunk_sectors;
 	time64_t			ctime, utime;
 	int				level, layout;
 	char				clevel[16];
···
 	 */
 	sector_t			reshape_position;
 	int				delta_disks, new_level, new_layout;
-	unsigned int			new_chunk_sectors;
+	int				new_chunk_sectors;
 	int				reshape_backwards;
 
 	struct md_thread		*thread;	/* management thread */