Re: [syzbot] [io-uring?] KCSAN: data-race in io_sq_thread / io_sq_thread_park (9)

[Jens Axboe <axboe@kernel.dk>]

On 8/13/24 2:50 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    6a0e38264012 Merge tag 'for-6.11-rc2-tag' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1019759d980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cb57e6ebf675f9d2
> dashboard link: https://syzkaller.appspot.com/bug?extid=2b946a3fd80caf971b21
> 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/753a842a966b/disk-6a0e3826.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/e12e23519777/vmlinux-6a0e3826.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/bce0584a8cb4/bzImage-6a0e3826.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2b946a3fd80caf971b21@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KCSAN: data-race in io_sq_thread / io_sq_thread_park
> 
> write to 0xffff888111459638 of 8 bytes by task 10761 on cpu 1:
>  io_sq_thread+0xdab/0xff0 io_uring/sqpoll.c:383
>  ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> read to 0xffff888111459638 of 8 bytes by task 10329 on cpu 0:
>  io_sq_thread_park+0x1b/0x80 io_uring/sqpoll.c:47
>  io_ring_exit_work+0x197/0x500 io_uring/io_uring.c:2786
>  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: 0xffff8881223d0000 -> 0x0000000000000000

It's just a debug check.

#syz test

diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
index b3722e5275e7..3b50dc9586d1 100644
--- a/io_uring/sqpoll.c
+++ b/io_uring/sqpoll.c
@@ -44,7 +44,7 @@ void io_sq_thread_unpark(struct io_sq_data *sqd)
 void io_sq_thread_park(struct io_sq_data *sqd)
 	__acquires(&sqd->lock)
 {
-	WARN_ON_ONCE(sqd->thread == current);
+	WARN_ON_ONCE(data_race(sqd->thread) == current);
 
 	atomic_inc(&sqd->park_pending);
 	set_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);

-- 
Jens Axboe