[PATCH 2/2] btrfs: do not write corrupted metadata blocks to disk

[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>
---
 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 4420ab2..cf85714 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -506,23 +506,34 @@ static int btree_read_extent_buffer_pages(struct btrfs_root *root,
 
 static int csum_dirty_buffer(struct btrfs_fs_info *fs_info, struct page *page)
 {
 	u64 start = page_offset(page);
 	u64 found_start;
 	struct extent_buffer *eb;
 
 	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);
 }
 
 static int check_tree_block_fsid(struct btrfs_fs_info *fs_info,
 				 struct extent_buffer *eb)
 {
 	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
 	u8 fsid[BTRFS_UUID_SIZE];
 	int ret = 1;
 
-- 
1.9.1