ovl: properly implement sync_filesystem()

overlayfs syncs all inode pages on sync_filesystem(), but it also
needs to call s_op->sync_fs() of upper fs for metadata sync.

This fixes correctness of syncfs(2) as demonstrated by following
xfs specific test:

xfs_sync_stats()
{
	echo $1
	echo -n "xfs_log_force = "
	grep log /proc/fs/xfs/stat  | awk '{ print $5 }'
}

xfs_sync_stats "before touch"
touch x
xfs_sync_stats "after touch"
xfs_io -c syncfs .
xfs_sync_stats "after syncfs"
xfs_io -c fsync x
xfs_sync_stats "after fsync"
xfs_io -c fsync x
xfs_sync_stats "after fsync #2"

When this test is run in overlay mount over xfs, log force
count does not increase with syncfs command.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 6792bb70b4ac1311f729fc166aba26d857b1b979..346f668e7df027e605d30ed971e26b90cecae38c 100644 (file)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -160,6 +160,25 @@ static void ovl_put_super(struct super_block *sb)
        kfree(ufs);
 }
 
+static int ovl_sync_fs(struct super_block *sb, int wait)
+{
+       struct ovl_fs *ufs = sb->s_fs_info;
+       struct super_block *upper_sb;
+       int ret;
+
+       if (!ufs->upper_mnt)
+               return 0;
+       upper_sb = ufs->upper_mnt->mnt_sb;
+       if (!upper_sb->s_op->sync_fs)
+               return 0;
+
+       /* real inodes have already been synced by sync_filesystem(ovl_sb) */
+       down_read(&upper_sb->s_umount);
+       ret = upper_sb->s_op->sync_fs(upper_sb, wait);
+       up_read(&upper_sb->s_umount);
+       return ret;
+}
+
 /**
  * ovl_statfs
  * @sb: The overlayfs super block
@@ -222,6 +241,7 @@ static int ovl_remount(struct super_block *sb, int *flags, char *data)
 
 static const struct super_operations ovl_super_operations = {
        .put_super      = ovl_put_super,
+       .sync_fs        = ovl_sync_fs,
        .statfs         = ovl_statfs,
        .show_options   = ovl_show_options,
        .remount_fs     = ovl_remount,