linux-kernel - [PATCH 4.5 125/128] Btrfs: fix empty symlink after creating symlink and fsync parent dir

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Date:	Sun,  5 Jun 2016 15:24:40 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Filipe Manana <fdmanana@...e.com>
Subject: [PATCH 4.5 125/128] Btrfs: fix empty symlink after creating symlink and fsync parent dir

4.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Filipe Manana <fdmanana@...e.com>

commit 3f9749f6e9edcf8ec569fb542efc3be35e06e84a upstream.

If we create a symlink, fsync its parent directory, crash/power fail and
mount the filesystem, we end up with an empty symlink, which not only is
useless it's also not allowed in linux (the man page symlink(2) is well
explicit about that).  So we just need to make sure to fully log an inode
if it's a symlink, to ensure its inline extent gets logged, ensuring the
same behaviour as ext3, ext4, xfs, reiserfs, f2fs, nilfs2, etc.

Example reproducer:

  $ mkfs.btrfs -f /dev/sdb
  $ mount /dev/sdb /mnt
  $ mkdir /mnt/testdir
  $ sync
  $ ln -s /mnt/foo /mnt/testdir/bar
  $ xfs_io -c fsync /mnt/testdir
  <power fail>
  $ mount /dev/sdb /mnt
  $ readlink /mnt/testdir/bar
  <empty string>

A test case for fstests follows soon.

Signed-off-by: Filipe Manana <fdmanana@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/btrfs/tree-log.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -5157,7 +5157,7 @@ process_leaf:
 			}

 			ctx->log_new_dentries = false;
-			if (type == BTRFS_FT_DIR)
+			if (type == BTRFS_FT_DIR || type == BTRFS_FT_SYMLINK)
 				log_mode = LOG_INODE_ALL;
 			btrfs_release_path(path);
 			ret = btrfs_log_inode(trans, root, di_inode,