From: ChangSyun Peng <allenpeng@synology.com>
Date: Fri, 31 Jul 2020 17:50:17 +0800
Subject: [PATCH] md/raid5: Fix Force reconstruct-write io stuck in degraded
 raid5
Git-commit: a1c6ae3d9f3dd6aa5981a332a6f700cf1c25edef
Patch-mainline: v5.9
References: git-fixes

In degraded raid5, we need to read parity to do reconstruct-write when
data disks fail. However, we can not read parity from
handle_stripe_dirtying() in force reconstruct-write mode.

Reproducible Steps:

1. Create degraded raid5
mdadm -C /dev/md2 --assume-clean -l5 -n3 /dev/sda2 /dev/sdb2 missing
2. Set rmw_level to 0
echo 0 > /sys/block/md2/md/rmw_level
3. IO to raid5

Now some io may be stuck in raid5. We can use handle_stripe_fill() to read
the parity in this situation.

Cc: <stable@vger.kernel.org> # v4.4+
Reviewed-by: Alex Wu <alexwu@synology.com>
Reviewed-by: BingJing Chang <bingjingc@synology.com>
Reviewed-by: Danny Shih <dannyshih@synology.com>
Signed-off-by: ChangSyun Peng <allenpeng@synology.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 drivers/md/raid5.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3613,6 +3613,7 @@ static int need_this_block(struct stripe
 	 * is missing/faulty, then we need to read everything we can.
 	 */
 	if (sh->raid_conf->level != 6 &&
+	    sh->raid_conf->rmw_level != PARITY_DISABLE_RMW &&
 	    sh->sector < sh->raid_conf->mddev->recovery_cp)
 		/* reconstruct-write isn't being forced */
 		return 0;
@@ -4848,7 +4849,7 @@ static void handle_stripe(struct stripe_
 	 * or to load a block that is being partially written.
 	 */
 	if (s.to_read || s.non_overwrite
-	    || (conf->level == 6 && s.to_write && s.failed)
+	    || (s.to_write && s.failed)
 	    || (s.syncing && (s.uptodate + s.compute < disks))
 	    || s.replacing
 	    || s.expanding)