Btrfs: fix btrfs_wait_ordered_range() so that it waits for all ordered extents

In btrfs_wait_ordered_range() once we find an ordered extent that has
finished with an error we exit the loop and don't wait for any other
ordered extents that might be still in progress.

All the users of btrfs_wait_ordered_range() expect that there are no more
ordered extents in progress after that function returns. So past fixes
such like the ones from the two following commits:

  ff612ba7 ("btrfs: fix panic during relocation after ENOSPC before
                   writeback happens")

  28aeeac1 ("Btrfs: fix panic when starting bg cache writeout after
                   IO error")

don't work when there are multiple ordered extents in the range.

Fix that by making btrfs_wait_ordered_range() wait for all ordered extents
even after it finds one that had an error.

Link: https://github.com/kdave/btrfs-progs/issues/228#issuecomment-569777554
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Signed-off-by: NFilipe Manana <fdmanana@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/ordered-data.c

@@ -679,10 +679,15 @@ int btrfs_wait_ordered_range(struct inode *inode, u64 start, u64 len)
 		}
 		btrfs_start_ordered_extent(inode, ordered, 1);
 		end = ordered->file_offset;
+		/*
+		 * If the ordered extent had an error save the error but don't
+		 * exit without waiting first for all other ordered extents in
+		 * the range to complete.
+		 */
 		if (test_bit(BTRFS_ORDERED_IOERR, &ordered->flags))
 			ret = -EIO;
 		btrfs_put_ordered_extent(ordered);
-		if (ret || end == 0 || end == start)
+		if (end == 0 || end == start)
 			break;
 		end--;
 	}