From 76b42abbf7488121c4f9f1ea5941123306e25d99 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Tue, 14 Feb 2017 16:56:01 +0000 Subject: [PATCH] Btrfs: fix data loss after truncate when using the no-holes feature If we have a file with an implicit hole (NO_HOLES feature enabled) that has an extent following the hole, delayed writes against regions of the file behind the hole happened before but were not yet flushed and then we truncate the file to a smaller size that lies inside the hole, we end up persisting a wrong disk_i_size value for our inode that leads to data loss after umounting and mounting again the filesystem or after the inode is evicted and loaded again. This happens because at inode.c:btrfs_truncate_inode_items() we end up setting last_size to the offset of the extent that we deleted and that followed the hole. We then pass that value to btrfs_ordered_update_i_size() which updates the inode's disk_i_size to a value smaller then the offset of the buffered (delayed) writes. Example reproducer: $ mkfs.btrfs -f /dev/sdb $ mount /dev/sdb /mnt $ xfs_io -f -c "pwrite -S 0x01 0K 32K" /mnt/foo $ xfs_io -d -c "pwrite -S 0x02 -b 32K 64K 32K" /mnt/foo $ xfs_io -c "truncate 60K" /mnt/foo --> inode's disk_i_size updated to 0 $ md5sum /mnt/foo 3c5ca3c3ab42f4b04d7e7eb0b0d4d806 /mnt/foo $ umount /dev/sdb $ mount /dev/sdb /mnt $ md5sum /mnt/foo d41d8cd98f00b204e9800998ecf8427e /mnt/foo --> Empty file, all data lost! Cc: # 3.14+ Fixes: 16e7549f045d ("Btrfs: incompatible format change to remove hole extents") Signed-off-by: Filipe Manana Reviewed-by: Liu Bo --- fs/btrfs/inode.c | 19 ++++++------------- 1 file changed, 6 insertions(+), 13 deletions(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 4efe9d82944c..70df45192424 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -4418,19 +4418,8 @@ search_again: if (found_type > min_type) { del_item = 1; } else { - if (item_end < new_size) { - /* - * With NO_HOLES mode, for the following mapping - * - * [0-4k][hole][8k-12k] - * - * if truncating isize down to 6k, it ends up - * isize being 8k. - */ - if (btrfs_fs_incompat(root->fs_info, NO_HOLES)) - last_size = new_size; + if (item_end < new_size) break; - } if (found_key.offset >= new_size) del_item = 1; else @@ -4613,8 +4602,12 @@ out: btrfs_abort_transaction(trans, ret); } error: - if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) + if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) { + ASSERT(last_size >= new_size); + if (!err && last_size > new_size) + last_size = new_size; btrfs_ordered_update_i_size(inode, last_size, NULL); + } btrfs_free_path(path); -- 2.39.5