In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix potential deadloop in prepare_compress_overwrite()
Jan Prusakowski reported a kernel hang issue as below:
When running xfstests on linux-next kernel (6.14.0-rc3, 6.12) I
encountered a problem in generic/475 test where fsstress process
gets blocked in __f2fs_write_data_pages() and the test hangs.
The options I used are:
MKFS_OPTIONS -- -O compression -O extra_attr -O project_quota -O quota /dev/vdc
MOUNT_OPTIONS -- -o acl,user_xattr -o discard,compress_extension=* /dev/vdc /vdc
INFO: task kworker/u8:0:11 blocked for more than 122 seconds.
Not tainted 6.14.0-rc3-xfstests-lockdep #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u8:0 state:D stack:0 pid:11 tgid:11 ppid:2 task_flags:0x4208160 flags:0x00004000
Workqueue: writeback wb_workfn (flush-253:0)
Call Trace:
<TASK>
__schedule+0x309/0x8e0
schedule+0x3a/0x100
schedule_preempt_disabled+0x15/0x30
__mutex_lock+0x59a/0xdb0
__f2fs_write_data_pages+0x3ac/0x400
do_writepages+0xe8/0x290
__writeback_single_inode+0x5c/0x360
writeback_sb_inodes+0x22f/0x570
wb_writeback+0xb0/0x410
wb_do_writeback+0x47/0x2f0
wb_workfn+0x5a/0x1c0
process_one_work+0x223/0x5b0
worker_thread+0x1d5/0x3c0
kthread+0xfd/0x230
ret_from_fork+0x31/0x50
ret_from_fork_asm+0x1a/0x30
</TASK>
The root cause is: once generic/475 starts toload error table to dm
device, f2fs_prepare_compress_overwrite() will loop reading compressed
cluster pages due to IO error, meanwhile it has held .writepages lock,
it can block all other writeback tasks.
Let's fix this issue w/ below changes:
- add f2fs_handle_page_eio() in prepare_compress_overwrite() to
detect IO error.
- detect cp_error earler in f2fs_read_multi_pages().
Publication date: Wed, 16 Apr 2025 14:13:00 +0000