dm mpath: verify __pg_init_all_paths locking assumptions at runtime

Verify at runtime that __pg_init_all_paths() is called with
multipath.lock held if lockdep is enabled.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index d85baff..730ec0b 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -298,6 +298,8 @@
 	struct pgpath *pgpath;
 	unsigned long pg_init_delay = 0;
 
+	lockdep_assert_held(&m->lock);
+
 	if (atomic_read(&m->pg_init_in_progress) || test_bit(MPATHF_PG_INIT_DISABLED, &m->flags))
 		return 0;