On Thu, Nov 05, 2015 at 09:57:35PM -0500, Jeff Mahoney wrote: > So now file_operations callbacks can't assume that file->f_path.dentry > belongs to the same file system that implements the callback. More than > that, any code that could ultimately get a dentry that comes from an > open file can't trust that it's from the same file system. Use file_inode() for inode. > This crash is due to this issue. Unlike xfs and ext2/3/4, we use > file->f_path.dentry->d_inode to resolve the inode. Using file_inode() > is an easy enough fix here, but we run into trouble later. We have > logic in the btrfs fsync() call path (check_parent_dirs_for_sync) that > walks back up the dentry chain examining the inode's last transaction > and last unlink transaction to determine whether a full transaction > commit is required. This obviously doesn't work if we're walking the > overlayfs path instead. Regardless of any argument over whether that's > doing the right thing, it's a pretty common pattern to assume that > file->f_path.dentry comes from the same file system when using a > file_operation. Is it intended that that assumption is no longer valid? It's actually rare, and your example is a perfect demonstration of the reasons why it is so rare. What's to protect btrfs_log_dentry_safe() from racing with rename(2)? Sure, you do dget_parent(). Which protects you from having one-time parent dentry freed under you. What it doesn't do is making any promises about its relationship with your file. -- To unsubscribe from this list: send the line "unsubscribe fstests" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
