dm raid: fix deadlock caused by premature md_stop_writes()

md_stop_writes() is called in raid_presuspend() causing deadlocks on
bios submitted afterwards -- which happens on loaded raid sets with
conversion requests.

Fix by moving md_stop_writes() to raid_postsuspend().  NOTE: when the
recovery's frozen (MD_RECOVERY_FROZEN), writes haven't been started (or
are already stopped) so don't stop them again.

Also remove superfluous readonly setting.
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-raid.c

@@ -3613,24 +3613,19 @@ static void raid_io_hints(struct dm_target *ti, struct queue_limits *limits)
 	blk_limits_io_opt(limits, chunk_size * mddev_data_stripes(rs));
 }
 
-static void raid_presuspend(struct dm_target *ti)
-{
-	struct raid_set *rs = ti->private;
-
-	md_stop_writes(&rs->md);
-}
-
 static void raid_postsuspend(struct dm_target *ti)
 {
 	struct raid_set *rs = ti->private;
 
 	if (!test_and_set_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags)) {
+		/* Writes have to be stopped before suspending to avoid deadlocks. */
+		if (!test_bit(MD_RECOVERY_FROZEN, &rs->md.recovery))
+			md_stop_writes(&rs->md);
+
 		mddev_lock_nointr(&rs->md);
 		mddev_suspend(&rs->md);
 		mddev_unlock(&rs->md);
 	}
-
-	rs->md.ro = 1;
 }
 
 static void attempt_restore_of_faulty_devices(struct raid_set *rs)
@@ -3903,7 +3898,6 @@ static struct target_type raid_target = {
 	.message = raid_message,
 	.iterate_devices = raid_iterate_devices,
 	.io_hints = raid_io_hints,
-	.presuspend = raid_presuspend,
 	.postsuspend = raid_postsuspend,
 	.preresume = raid_preresume,
 	.resume = raid_resume,