[PATCH 12/17] btrfs: do not write corrupted metadata blocks to disk

[David Sterba <dsterba@suse.com>]

From: Alex Lyakas <alex.bolshoy@gmail.com>

csum_dirty_buffer was issuing a warning in case the extent buffer
did not look alright, but was still returning success.
Let's return error in this case, and also add an additional sanity
check on the extent buffer header.
The caller up the chain may BUG_ON on this, for example flush_epd_write_bio will,
but it is better than to have a silent metadata corruption on disk.

Signed-off-by: Alex Lyakas <alex@zadarastorage.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/disk-io.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 87946c69c68f..ae6e3e36fdf0 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -513,9 +513,20 @@ static int csum_dirty_buffer(struct btrfs_fs_info *fs_info, struct page *page)
 	eb = (struct extent_buffer *)page->private;
 	if (page != eb->pages[0])
 		return 0;
+
 	found_start = btrfs_header_bytenr(eb);
-	if (WARN_ON(found_start != start || !PageUptodate(page)))
-		return 0;
+	/*
+	 * Please do not consolidate these warnings into a single if.
+	 * It is useful to know what went wrong.
+	 */
+	if (WARN_ON(found_start != start))
+		return -EUCLEAN;
+	if (WARN_ON(!PageUptodate(page)))
+		return -EUCLEAN;
+
+	ASSERT(memcmp_extent_buffer(eb, fs_info->fsid,
+			btrfs_header_fsid(), BTRFS_FSID_SIZE) == 0);
+
 	return csum_tree_block(fs_info, eb, 0);
 }
 
-- 
2.7.1