f2fs: Prevent swap file in LFS mode

The kernel writes to swap files on f2fs directly without the assistance
of the filesystem. This direct write by kernel can be non-sequential
even when the f2fs is in LFS mode. Such non-sequential write conflicts
with the LFS semantics. Especially when f2fs is set up on zoned block
devices, the non-sequential write causes unaligned write command errors.

To avoid the non-sequential writes to swap files, prevent swap file
activation when the filesystem is in LFS mode.

Fixes: 4969c06a ("f2fs: support swap file w/ DIO")
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Cc: stable@vger.kernel.org # v5.10+
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -4076,6 +4076,12 @@ static int f2fs_swap_activate(struct swap_info_struct *sis, struct file *file,
 	if (f2fs_readonly(F2FS_I_SB(inode)->sb))
 		return -EROFS;
 
+	if (f2fs_lfs_mode(F2FS_I_SB(inode))) {
+		f2fs_err(F2FS_I_SB(inode),
+			"Swapfile not supported in LFS mode");
+		return -EINVAL;
+	}
+
 	ret = f2fs_convert_inline_inode(inode);
 	if (ret)
 		return ret;