[moderation] [perf?] KCSAN: data-race in detach_pid / perf_event_switch_output (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dbf00d8d23b4 Merge tag 'fs_for_v7.0-rc7' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10ac0dda580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3a78dd265deac3a9
dashboard link: https://syzkaller.appspot.com/bug?extid=f9f3a7d6c14160cbfbef
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [ac...@kernel.org adrian...@intel.com alexander...@linux.intel.com iro...@google.com james...@linaro.org jo...@kernel.org linux-...@vger.kernel.org linux-pe...@vger.kernel.org mark.r...@arm.com mi...@redhat.com namh...@kernel.org pet...@infradead.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/70651e7c1647/disk-dbf00d8d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0543b653e8d0/vmlinux-dbf00d8d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ed09c0a4c42d/bzImage-dbf00d8d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f9f3a7...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in detach_pid / perf_event_switch_output

write to 0xffff88811a1d2798 of 8 bytes by task 5621 on cpu 1:
__change_pid kernel/pid.c:405 [inline]
detach_pid+0xf0/0x1a0 kernel/pid.c:417
__unhash_process kernel/exit.c:141 [inline]
__exit_signal kernel/exit.c:212 [inline]
release_task+0x65b/0xb60 kernel/exit.c:265
wait_task_zombie kernel/exit.c:1280 [inline]
wait_consider_task+0x1160/0x1670 kernel/exit.c:1507
do_wait_thread kernel/exit.c:1570 [inline]
__do_wait+0xf9/0x510 kernel/exit.c:1688
do_wait+0xb6/0x260 kernel/exit.c:1722
kernel_wait4+0x19f/0x210 kernel/exit.c:1881
__do_sys_wait4 kernel/exit.c:1909 [inline]
__se_sys_wait4 kernel/exit.c:1905 [inline]
__x64_sys_wait4+0x91/0x120 kernel/exit.c:1905
x64_sys_call+0x2aee/0x3020 arch/x86/include/generated/asm/syscalls_64.h:62
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a1d2798 of 8 bytes by task 3000 on cpu 0:
pid_alive include/linux/pid.h:267 [inline]
perf_event_pid_type kernel/events/core.c:1533 [inline]
perf_event_pid kernel/events/core.c:1540 [inline]
perf_event_switch_output+0x1a4/0x3a0 kernel/events/core.c:10029
perf_iterate_sb_cpu kernel/events/core.c:8922 [inline]
perf_iterate_sb+0x368/0x650 kernel/events/core.c:8951
perf_event_switch kernel/events/core.c:10076 [inline]
__perf_event_task_sched_in+0xa2c/0xad0 kernel/events/core.c:4322
perf_event_task_sched_in include/linux/perf_event.h:1639 [inline]
finish_task_switch+0x1f8/0x280 kernel/sched/core.c:5150
context_switch kernel/sched/core.c:5301 [inline]
__schedule+0x93c/0xd40 kernel/sched/core.c:6911
__schedule_loop kernel/sched/core.c:6993 [inline]
schedule+0x5e/0xd0 kernel/sched/core.c:7008
schedule_hrtimeout_range_clock+0xd5/0x1a0 kernel/time/sleep_timeout.c:216
schedule_hrtimeout_range+0x28/0x40 kernel/time/sleep_timeout.c:263
ep_poll fs/eventpoll.c:2028 [inline]
do_epoll_wait+0x854/0x950 fs/eventpoll.c:2462
__do_sys_epoll_wait fs/eventpoll.c:2470 [inline]
__se_sys_epoll_wait fs/eventpoll.c:2465 [inline]
__x64_sys_epoll_wait+0x15e/0x190 fs/eventpoll.c:2465
x64_sys_call+0x273e/0x3020 arch/x86/include/generated/asm/syscalls_64.h:233
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888103f1a0c0 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3000 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup