[moderation] [kernel?] KCSAN: data-race in copy_process / futex_hash_allocate_default

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7a0892d2836e Merge tag 'pci-v6.18-fixes-5' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11c15c12580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d2e0bc0ae94545f7
dashboard link: https://syzkaller.appspot.com/bug?extid=e2b0566187a4bfc4e388
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [andre...@igalia.com da...@stgolabs.net dvh...@infradead.org linux-...@vger.kernel.org mi...@redhat.com pet...@infradead.org tg...@linutronix.de]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6a84521b0472/disk-7a0892d2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/318d824bb6a5/vmlinux-7a0892d2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6f5a3b6df25e/bzImage-7a0892d2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e2b056...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in copy_process / futex_hash_allocate_default

read-write to 0xffff888121ba5688 of 4 bytes by task 6435 on cpu 1:
copy_process+0x1a8b/0x2000 kernel/fork.c:2403
create_io_thread+0x71/0xa0 kernel/fork.c:2557
create_io_worker+0xe0/0x370 io_uring/io-wq.c:910
io_wq_create_worker io_uring/io-wq.c:339 [inline]
io_wq_enqueue+0x2c1/0x3a0 io_uring/io-wq.c:1037
io_queue_iowq+0x201/0x2e0 io_uring/io_uring.c:524
io_req_task_submit+0xc4/0x100 io_uring/io_uring.c:1464
__io_run_local_work_loop io_uring/io_uring.c:1379 [inline]
__io_run_local_work+0x26c/0x4f0 io_uring/io_uring.c:1412
io_run_local_work io_uring/io_uring.c:1445 [inline]
io_cqring_wait io_uring/io_uring.c:2727 [inline]
__do_sys_io_uring_enter io_uring/io_uring.c:3553 [inline]
__se_sys_io_uring_enter+0x144b/0x1b70 io_uring/io_uring.c:3453
__x64_sys_io_uring_enter+0x78/0x90 io_uring/io_uring.c:3453
x64_sys_call+0x2df0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:427
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888121ba5688 of 4 bytes by task 6434 on cpu 0:
get_nr_threads include/linux/sched/signal.h:701 [inline]
futex_hash_allocate_default+0x5b/0x190 kernel/futex/core.c:1898
copy_process+0x151e/0x2000 kernel/fork.c:2302
kernel_clone+0x16c/0x5c0 kernel/fork.c:2609
__do_sys_clone3 kernel/fork.c:2911 [inline]
__se_sys_clone3+0x1c2/0x200 kernel/fork.c:2890
__x64_sys_clone3+0x31/0x40 kernel/fork.c:2890
x64_sys_call+0x1fc9/0x3000 arch/x86/include/generated/asm/syscalls_64.h:436
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000003 -> 0x00000004

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 6434 Comm: syz.1.1228 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


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