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

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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 41a2ee75aa ("btrfs: introduce
per-inode file extent tree"), then became hidden since commit 3d7db6e8bd
("btrfs: don't allocate file extent tree for non regular files") and then
visible again after commit 8679d2687c ("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
fallocate -n -o 1M -l 2M $MNT/file1

umount $MNT
mount $DEV $MNT

len=$((1 * 1024 * 1024))

fallocate -o 1M -l $len $MNT/file1

du --bytes $MNT/file1

umount $MNT
mount $DEV $MNT

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: 41a2ee75aa ("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>
This commit is contained in:
austinchang 2025-10-29 09:35:27 +00:00 committed by David Sterba
parent 953902e4fb
commit 3b1a4a59a2
1 changed files with 10 additions and 0 deletions
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10
fs/btrfs/file.c
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@ -2854,12 +2854,22 @@ 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);