dm btree: silence lockdep lock inversion in dm_btree_del()

Allocate memory using GFP_NOIO when deleting a btree. dm_btree_del()
can be called via an ioctl and we don't want to recurse into the FS or
block layer.

Signed-off-by: Joe Thornber <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>
Cc: [e-mail]

drivers/md/persistent-data/dm-btree.c

···
 	int r;
 	struct del_stack *s;
 
-	s = kmalloc(sizeof(*s), GFP_KERNEL);
+	s = kmalloc(sizeof(*s), GFP_NOIO);
 	if (!s)
 		return -ENOMEM;
 	s->info = info;