[syzbot] [io-uring?] KCSAN: data-race in io_recv / io_wq_free_work

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 150b567e0d57 Merge tag 'net-6.13-rc3' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1013cd44580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1fe4854f351e948c
dashboard link: https://syzkaller.appspot.com/bug?extid=a697a4754324488bacd7
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/05e47d657c7d/disk-150b567e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/568329a94d6e/vmlinux-150b567e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/eab7b6a3d180/bzImage-150b567e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a697a4...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in io_recv / io_wq_free_work

write to 0xffff88814248b848 of 8 bytes by task 22395 on cpu 1:
io_recv+0x661/0xa70
io_issue_sqe+0x150/0xc10 io_uring/io_uring.c:1736
io_poll_issue+0x1a/0x20 io_uring/io_uring.c:1767
io_poll_check_events io_uring/poll.c:289 [inline]
io_poll_task_func+0x205/0x7c0 io_uring/poll.c:316
io_handle_tw_list+0xe3/0x200 io_uring/io_uring.c:1053
tctx_task_work_run+0x6e/0x1c0 io_uring/io_uring.c:1117
tctx_task_work+0x40/0x80 io_uring/io_uring.c:1135
task_work_run+0x13a/0x1a0 kernel/task_work.c:239
io_run_task_work+0x1b1/0x200 io_uring/io_uring.h:343
io_cqring_wait io_uring/io_uring.c:2594 [inline]
__do_sys_io_uring_enter io_uring/io_uring.c:3434 [inline]
__se_sys_io_uring_enter+0x14f5/0x1ba0 io_uring/io_uring.c:3325
__x64_sys_io_uring_enter+0x78/0x90 io_uring/io_uring.c:3325
x64_sys_call+0xb5e/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:427
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88814248b848 of 8 bytes by task 22396 on cpu 0:
req_ref_put_and_test io_uring/refs.h:22 [inline]
io_wq_free_work+0x24/0x1b0 io_uring/io_uring.c:1776
io_worker_handle_work+0x4cb/0x9d0 io_uring/io-wq.c:604
io_wq_worker+0x286/0x820 io_uring/io-wq.c:655
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: 0x0000000085584038 -> 0x0000000085184138

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 22396 Comm: iou-wrk-22395 Not tainted 6.13.0-rc2-syzkaller-00130-g150b567e0d57 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
==================================================================


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[Pavel Begunkov]

IIUC what that it, it's known and mild. Writes to flags are
synchronised, for concurrent reads we make sure the interesting
bits are set in advance. i.e. only a problem if compiler decides
to mask a bit while modifying an unrelated bit or so. We probably
need WRITE_ONCE or splitting flags into two sets.

--
Pavel Begunkov

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.