btrfs: fix missing increment of bi_remaining

In btrfs_end_bio(), we increment bi_remaining if is_orig_bio. If not,
we restore the orig_bio but failed to increment bi_remaining for
orig_bio, which triggers a BUG_ON later when bio_endio is called. Fix
is to increment bi_remaining when we restore the orig bio as well.
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
CC: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: Muthukumar Ratty <muthur@gmail.com>
Reviewed-by: Chris Mason <clm@fb.com>
Tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/btrfs/volumes.c

@@ -5297,9 +5297,14 @@ static void btrfs_end_bio(struct bio *bio, int err)
 		if (!is_orig_bio) {
 			bio_put(bio);
 			bio = bbio->orig_bio;
-		} else {
-			atomic_inc(&bio->bi_remaining);
 		}
+
+ 		/*
+		 * We have original bio now. So increment bi_remaining to
+		 * account for it in endio
+		 */
+		atomic_inc(&bio->bi_remaining);
+
 		bio->bi_private = bbio->private;
 		bio->bi_end_io = bbio->end_io;
 		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;