[moderation] [kernel?] KCSAN: data-race in print_cpu / tick_nohz_stop_idle (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2d3090a8aeb5 Merge tag 'v7.1-p5' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17ec257a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f571f22917457cd8
dashboard link: https://syzkaller.appspot.com/bug?extid=dbed1aeceff803ffc284
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [anna-...@linutronix.de fred...@kernel.org linux-...@vger.kernel.org mi...@kernel.org tg...@kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/26be1447042c/disk-2d3090a8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/670d370f999e/vmlinux-2d3090a8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c666178a2688/bzImage-2d3090a8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+dbed1a...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in print_cpu / tick_nohz_stop_idle

read-write to 0xffff888237c1be98 of 8 bytes by interrupt on cpu 0:
tick_sched_flag_clear kernel/time/tick-sched.c:201 [inline]
tick_nohz_stop_idle+0xde/0x130 kernel/time/tick-sched.c:770
tick_nohz_irq_enter kernel/time/tick-sched.c:1572 [inline]
tick_irq_enter+0x8d/0x100 kernel/time/tick-sched.c:1598
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
sysvec_apic_timer_interrupt+0x67/0x80 arch/x86/kernel/apic/apic.c:1061
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:62
arch_safe_halt arch/x86/kernel/process.c:766 [inline]
default_idle+0x9/0x20 arch/x86/kernel/process.c:767
default_idle_call+0x3b/0x60 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:199 [inline]
do_idle+0x17f/0x2b0 kernel/sched/idle.c:352
cpu_startup_entry+0x24/0x30 kernel/sched/idle.c:451
rest_init+0xee/0xf0 init/main.c:762
start_kernel+0x49f/0x4d0 init/main.c:1220
x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
x86_64_start_kernel+0xfc/0x100 arch/x86/kernel/head64.c:291
common_startup_64+0x13e/0x147

read to 0xffff888237c1be98 of 8 bytes by task 5840 on cpu 1:
print_cpu+0x3df/0x670 kernel/time/timer_list.c:151
timer_list_show+0x107/0x170 kernel/time/timer_list.c:291
seq_read_iter+0x636/0x940 fs/seq_file.c:273
proc_reg_read_iter+0x110/0x180 fs/proc/inode.c:299
copy_splice_read+0x471/0x6c0 fs/splice.c:362
do_splice_read fs/splice.c:980 [inline]
splice_direct_to_actor+0x26e/0x670 fs/splice.c:1084
do_splice_direct_actor fs/splice.c:1202 [inline]
do_splice_direct+0x119/0x1a0 fs/splice.c:1228
do_sendfile+0x382/0x650 fs/read_write.c:1372
__do_sys_sendfile64 fs/read_write.c:1433 [inline]
__se_sys_sendfile64 fs/read_write.c:1419 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1419
x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000035 -> 0x0000000000000030

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5840 Comm: syz.5.594 Tainted: G W syzkaller #0 PREEMPT(lazy)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================


---
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