btrfs: warn if extent buffer mapping crosses a page boundary in csum_tree_block

Since commit d2e174d5d3ee ("btrfs: document extent mapping assumptions in
checksum") we have a comment in place why map_private_extent_buffer()
can't return 1 in the csum_tree_block() case.

Make this a bit more explicit and WARN_ON() in case this this assumption
breaks.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 4f11a83304aeae25d565b9126c7f033d6a65da98..c4404e1e9cfbaf5cff2bf52a44731075a6c313cf 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -285,7 +285,7 @@ static int csum_tree_block(struct extent_buffer *buf, u8 *result)
                 */
                err = map_private_extent_buffer(buf, offset, 32,
                                        &kaddr, &map_start, &map_len);
-               if (err)
+               if (WARN_ON(err))
                        return err;
                cur_len = min(len, map_len - (offset - map_start));
                crc = btrfs_csum_data(kaddr + offset - map_start,