dm raid: fix stripe adding reshape deadlock

When initiating a stripe adding reshape, a deadlock between
md_stop_writes() waiting for the sync thread to stop and the running
sync thread waiting for inactive stripes occurs (this frequently happens
on single-core but rarely on multi-core systems).

Fix this deadlock by setting MD_RECOVERY_WAIT to have the main MD
resynchronization thread worker (md_do_sync()) bail out when initiating
the reshape via constructor arguments.

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-raid.c

@@ -3869,14 +3869,13 @@ static int rs_start_reshape(struct raid_set *rs)
 	struct mddev *mddev = &rs->md;
 	struct md_personality *pers = mddev->pers;
 
+	/* Don't allow the sync thread to work until the table gets reloaded. */
+	set_bit(MD_RECOVERY_WAIT, &mddev->recovery);
+
 	r = rs_setup_reshape(rs);
 	if (r)
 		return r;
 
-	/* Need to be resumed to be able to start reshape, recovery is frozen until raid_resume() though */
-	if (test_and_clear_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags))
-		mddev_resume(mddev);
-
 	/*
 	 * Check any reshape constraints enforced by the personalility
 	 *
@@ -3900,10 +3899,6 @@ static int rs_start_reshape(struct raid_set *rs)
 		}
 	}
 
-	/* Suspend because a resume will happen in raid_resume() */
-	set_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags);
-	mddev_suspend(mddev);
-
 	/*
 	 * Now reshape got set up, update superblocks to
 	 * reflect the fact so that a table reload will