The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From bf504110bc8aa05df48b0e5f0aa84bfb81e0574b Mon Sep 17 00:00:00 2001

From: Filipe Manana fdmanana@suse.com Date: Mon, 4 Mar 2019 14:06:12 +0000 Subject: [PATCH] Btrfs: fix incorrect file size after shrinking truncate and fsync

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 commit 1a4bcf470c886b ("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 commit d4682ba03ef618 ("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

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index f06454a55e00..5256cddf3a43 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -4544,6 +4544,19 @@ static int logged_inode_size(struct btrfs_root *log, struct btrfs_inode *inode, item = btrfs_item_ptr(path->nodes[0], path->slots[0], struct btrfs_inode_item); *size_ret = btrfs_inode_size(path->nodes[0], item); + /* + * If the in-memory inode's i_size is smaller then the inode + * size stored in the btree, return the inode's i_size, so + * that we get a correct inode size after replaying the log + * when before a power failure we had a shrinking truncate + * followed by addition of a new name (rename / new hard link). + * Otherwise return the inode size from the btree, to avoid + * data loss when replaying a log due to previously doing a + * write that expands the inode's size and logging a new name + * immediately after. + */ + if (*size_ret > inode->vfs_inode.i_size) + *size_ret = inode->vfs_inode.i_size; }

btrfs_release_path(path);