Btrfs: fix xattr loss after power failure

If a file has xattrs, we fsync it, to ensure we clear the flags
BTRFS_INODE_NEEDS_FULL_SYNC and BTRFS_INODE_COPY_EVERYTHING from its
inode, the current transaction commits and then we fsync it (without
either of those bits being set in its inode), we end up not logging
all its xattrs. This results in deleting all xattrs when replying the
log after a power failure.

Trivial reproducer

  $ mkfs.btrfs -f /dev/sdb
  $ mount /dev/sdb /mnt

  $ touch /mnt/foobar
  $ setfattr -n user.xa -v qwerty /mnt/foobar
  $ xfs_io -c "fsync" /mnt/foobar

  $ sync

  $ xfs_io -c "pwrite -S 0xab 0 64K" /mnt/foobar
  $ xfs_io -c "fsync" /mnt/foobar
  <power failure>

  $ mount /dev/sdb /mnt
  $ getfattr --absolute-names --dump /mnt/foobar
  <empty output>
  $

So fix this by making sure all xattrs are logged if we log a file's inode
item and neither the flags BTRFS_INODE_NEEDS_FULL_SYNC nor
BTRFS_INODE_COPY_EVERYTHING were set in the inode.

Fixes: 36283bf777d9 ("Btrfs: fix fsync xattr loss in the fast fsync path")
Cc: <stable@vger.kernel.org> # 4.2+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -4827,6 +4827,7 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans,
 	struct extent_map_tree *em_tree = &inode->extent_tree;
 	u64 logged_isize = 0;
 	bool need_log_inode_item = true;
+	bool xattrs_logged = false;
 
 	path = btrfs_alloc_path();
 	if (!path)
@@ -5128,6 +5129,7 @@ next_key:
 	err = btrfs_log_all_xattrs(trans, root, inode, path, dst_path);
 	if (err)
 		goto out_unlock;
+	xattrs_logged = true;
 	if (max_key.type >= BTRFS_EXTENT_DATA_KEY && !fast_search) {
 		btrfs_release_path(path);
 		btrfs_release_path(dst_path);
@@ -5140,6 +5142,11 @@ log_extents:
 	btrfs_release_path(dst_path);
 	if (need_log_inode_item) {
 		err = log_inode_item(trans, log, dst_path, inode);
+		if (!err && !xattrs_logged) {
+			err = btrfs_log_all_xattrs(trans, root, inode, path,
+						   dst_path);
+			btrfs_release_path(path);
+		}
 		if (err)
 			goto out_unlock;
 	}