btrfs: mark dirty extent range for out of bound prealloc extents

In btrfs_fallocate(), when the allocated range overlaps with a prealloc
extent and the extent starts after i_size, the range doesn't get marked
dirty in file_extent_tree. This results in persisting an incorrect
disk_i_size for the inode when not using the no-holes feature.

This is reproducible since commit 41a2ee7 ("btrfs: introduce
per-inode file extent tree"), then became hidden since commit 3d7db6e
("btrfs: don't allocate file extent tree for non regular files") and then
visible again after commit 8679d26 ("btrfs: initialize
inode::file_extent_tree after i_mode has been set"), which fixes the
previous commit.

The following reproducer triggers the problem:

  $ cat test.sh

  MNT=/mnt/test
  DEV=/dev/vdb

  mkdir -p $MNT

  mkfs.btrfs -f -O ^no-holes $DEV
  mount $DEV $MNT

  touch $MNT/file1
  # Add a 2M extent at the file offset 1M without increasing i_size.
  fallocate -n -o 1M -l 2M $MNT/file1

  # Unmount and mount again to clear the in-memory extent tree.
  umount $MNT
  mount $DEV $MNT

  # Use a length that fits within the range of the previously allocated
  # extent. We want the next fallocate to only increase the i_size.
  len=$((1 * 1024 * 1024))

  # fallocate on the prealloc extent to change i_size.
  fallocate -o 1M -l $len $MNT/file1

  # Check the file size, expecting 2M.
  du --bytes $MNT/file1

  # Unmount and mount again the fs.
  umount $MNT
  mount $DEV $MNT

  # The file size should be the same as before (2M).
  du --bytes $MNT/file1

  umount $MNT

Running the reproducer gives the following result:

  $ ./test.sh
  (...)
  2097152 /mnt/test/file1
  1048576 /mnt/test/file1

The difference is exactly 1048576 as we assigned.

Fix by adding a call to btrfs_inode_set_file_extent_range() in
btrfs_fallocate_update_isize().

Fixes: 41a2ee7 ("btrfs: introduce per-inode file extent tree")
Signed-off-by: austinchang <austinchang@synology.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: austin880625syno

fs/btrfs/file.c

@@ -2857,12 +2857,22 @@ static int btrfs_fallocate_update_isize(struct inode *inode,
 {
 	struct btrfs_trans_handle *trans;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
+	u64 range_start;
+	u64 range_end;
 	int ret;
 	int ret2;
 
 	if (mode & FALLOC_FL_KEEP_SIZE || end <= i_size_read(inode))
 		return 0;
 
+	range_start = round_down(i_size_read(inode), root->fs_info->sectorsize);
+	range_end = round_up(end, root->fs_info->sectorsize);
+
+	ret = btrfs_inode_set_file_extent_range(BTRFS_I(inode), range_start,
+						range_end - range_start);
+	if (ret)
+		return ret;
+
 	trans = btrfs_start_transaction(root, 1);
 	if (IS_ERR(trans))
 		return PTR_ERR(trans);