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commitbf504110bcupstream. If we do a shrinking truncate against an inode which is already present in the respective log tree and then rename it, as part of logging the new name we end up logging an inode item that reflects the old size of the file (the one which we previously logged) and not the new smaller size. The decision to preserve the size previously logged was added by commit1a4bcf470c("Btrfs: fix fsync data loss after adding hard link to inode") in order to avoid data loss after replaying the log. However that decision is only needed for the case the logged inode size is smaller then the current size of the inode, as explained in that commit's change log. If the current size of the inode is smaller then the previously logged size, we know a shrinking truncate happened and therefore need to use that smaller size. Example to trigger the problem: $ mkfs.btrfs -f /dev/sdb $ mount /dev/sdb /mnt $ xfs_io -f -c "pwrite -S 0xab 0 8000" /mnt/foo $ xfs_io -c "fsync" /mnt/foo $ xfs_io -c "truncate 3000" /mnt/foo $ mv /mnt/foo /mnt/bar $ xfs_io -c "fsync" /mnt/bar <power failure> $ mount /dev/sdb /mnt $ od -t x1 -A d /mnt/bar 0000000 ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab * 0008000 Once we rename the file, we log its name (and inode item), and because the inode was already logged before in the current transaction, we log it with a size of 8000 bytes because that is the size we previously logged (with the first fsync). As part of the rename, besides logging the inode, we do also sync the log, which is done since commitd4682ba03e("Btrfs: sync log after logging new name"), so the next fsync against our inode is effectively a no-op, since no new changes happened since the rename operation. Even if did not sync the log during the rename operation, the same problem (fize size of 8000 bytes instead of 3000 bytes) would be visible after replaying the log if the log ended up getting synced to disk through some other means, such as for example by fsyncing some other modified file. In the example above the fsync after the rename operation is there just because not every filesystem may guarantee logging/journalling the inode (and syncing the log/journal) during the rename operation, for example it is needed for f2fs, but not for ext4 and xfs. Fix this scenario by, when logging a new name (which is triggered by rename and link operations), using the current size of the inode instead of the previously logged inode size. A test case for fstests follows soon. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=202695 CC: stable@vger.kernel.org # 4.4+ Reported-by: Seulbae Kim <seulbae@gatech.edu> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.