[PATCH v3 5/5] btrfs: Do mandatory tree block check before submitting bio

[Qu Wenruo <wqu@suse.com>]

There are at least 2 reports about memory bit flip sneaking into on-disk
data.

Currently we only have a relaxed check triggered at
btrfs_mark_buffer_dirty() time, as it's not mandatory, only for
CONFIG_BTRFS_FS_CHECK_INTEGRITY enabled build.

This patch will address the hole by triggering comprehensive check on
tree blocks before writing it back to disk.

The timing is set to csum_tree_block() where @verify == 0.
At that timing, we're generating csum for tree blocks before submitting
the metadata bio, so we could avoid all the unnecessary calls at
btrfs_mark_buffer_dirty(), but still catch enough error.

The example error output will be something like:
  BTRFS critical (device dm-3): corrupt leaf: root=2 block=1350630375424 slot=68, bad key order, prev (10510212874240 169 0) current (1714119868416 169 0)
  BTRFS error (device dm-3): write time tree block corruption detected
  BTRFS critical (device dm-3): corrupt leaf: root=2 block=1350630375424 slot=68, bad key order, prev (10510212874240 169 0) current (1714119868416 169 0)
  BTRFS error (device dm-3): write time tree block corruption detected
  BTRFS: error (device dm-3) in btrfs_commit_transaction:2220: errno=-5 IO failure (Error while writing out transaction)
  BTRFS info (device dm-3): forced readonly
  BTRFS warning (device dm-3): Skipping commit of aborted transaction.
  BTRFS: error (device dm-3) in cleanup_transaction:1839: errno=-5 IO failure
  BTRFS info (device dm-3): delayed_refs has NO entry

Reported-by: Leonard Lausen <leonard@lausen.nl>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/disk-io.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 426e9f450f70..68d75a3b15c5 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -313,6 +313,15 @@ static int csum_tree_block(struct btrfs_fs_info *fs_info,
 			return -EUCLEAN;
 		}
 	} else {
+		if (btrfs_header_level(buf))
+			err = btrfs_check_node(fs_info, buf);
+		else
+			err = btrfs_check_leaf_full(fs_info, buf);
+		if (err < 0) {
+			btrfs_err(fs_info,
+				  "write time tree block corruption detected");
+			return err;
+		}
 		write_extent_buffer(buf, result, 0, csum_size);
 	}
 
-- 
2.20.1