From: austinchang <austinchang@synology.com>
Date: Wed, 29 Oct 2025 09:35:27 +0000 (+0000)
Subject: btrfs: mark dirty extent range for out of bound prealloc extents
X-Git-Tag: v6.12.58~103
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6125acdf9aceb8be86c5dea473e9b800c60a5d86;p=thirdparty%2Fkernel%2Fstable.git

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

[ Upstream commit 3b1a4a59a2086badab391687a6a0b86e03048393 ]

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 41a2ee75aab0 ("btrfs: introduce
per-inode file extent tree"), then became hidden since commit 3d7db6e8bd22
("btrfs: don't allocate file extent tree for non regular files") and then
visible again after commit 8679d2687c35 ("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: 41a2ee75aab0 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 0e63603ac5c78..9ed2771f303c9 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2839,12 +2839,22 @@ 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);