Re: [syzbot] [io-uring?] KCSAN: data-race in __flush_work / __flush_work (2)

[Jens Axboe <axboe@kernel.dk>]

On 8/5/24 12:53 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    a5dbd76a8942 Merge tag 'x86-urgent-2024-08-04' of git://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13d5a373980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d16924117a4f7e9
> dashboard link: https://syzkaller.appspot.com/bug?extid=b3e4f2f51ed645fd5df2
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/ba663ad5dbf5/disk-a5dbd76a.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/226a427d6581/vmlinux-a5dbd76a.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/9f982777516a/bzImage-a5dbd76a.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b3e4f2f51ed645fd5df2@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KCSAN: data-race in __flush_work / __flush_work
> 
> write to 0xffff8881223aa3e8 of 8 bytes by task 3998 on cpu 0:
>  instrument_write include/linux/instrumented.h:41 [inline]
>  ___set_bit include/asm-generic/bitops/instrumented-non-atomic.h:28 [inline]
>  insert_wq_barrier kernel/workqueue.c:3790 [inline]
>  start_flush_work kernel/workqueue.c:4142 [inline]
>  __flush_work+0x30b/0x570 kernel/workqueue.c:4178
>  flush_work kernel/workqueue.c:4229 [inline]
>  flush_delayed_work+0x66/0x70 kernel/workqueue.c:4251
>  io_fallback_tw+0x24b/0x320 io_uring/io_uring.c:1087
>  tctx_task_work_run+0xd1/0x1b0 io_uring/io_uring.c:1099
>  tctx_task_work+0x40/0x80 io_uring/io_uring.c:1124
>  task_work_run+0x13a/0x1a0 kernel/task_work.c:228
>  exit_task_work include/linux/task_work.h:40 [inline]
>  do_exit+0x5dd/0x1720 kernel/exit.c:882
>  do_group_exit+0x102/0x150 kernel/exit.c:1031
>  get_signal+0xf2f/0x1080 kernel/signal.c:2917
>  arch_do_signal_or_restart+0x95/0x4b0 arch/x86/kernel/signal.c:310
>  exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
>  exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
>  syscall_exit_to_user_mode+0x59/0x130 kernel/entry/common.c:218
>  do_syscall_64+0xd6/0x1c0 arch/x86/entry/common.c:89
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> read to 0xffff8881223aa3e8 of 8 bytes by task 50 on cpu 1:
>  __flush_work+0x42a/0x570 kernel/workqueue.c:4188
>  flush_work kernel/workqueue.c:4229 [inline]
>  flush_delayed_work+0x66/0x70 kernel/workqueue.c:4251
>  io_uring_try_cancel_requests+0x35b/0x370 io_uring/io_uring.c:3000
>  io_ring_exit_work+0x148/0x500 io_uring/io_uring.c:2779
>  process_one_work kernel/workqueue.c:3231 [inline]
>  process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3312
>  worker_thread+0x526/0x700 kernel/workqueue.c:3390
>  kthread+0x1d1/0x210 kernel/kthread.c:389
>  ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> value changed: 0x0000000000400000 -> 0xffff88810006c00d
> 
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 UID: 0 PID: 50 Comm: kworker/u8:3 Not tainted 6.11.0-rc1-syzkaller-00334-ga5dbd76a8942 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
> Workqueue: iou_exit io_ring_exit_work
> ==================================================================

This looks like workqueue, CC'ing maintainers. Unsure if this is benign
or not.

#syz set subsystems: kernel

-- 
Jens Axboe