[moderation] [kernel?] KCSAN: data-race in ktime_get_ts64 / timekeeping_update_from_shadow

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 917719c412c4 Merge tag 'selinux-pr-20260507' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1680df48580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2e40c0f41e01837e
dashboard link: https://syzkaller.appspot.com/bug?extid=e5a59428bbf2722641f7
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [jst...@google.com linux-...@vger.kernel.org sb...@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/e55e13d50f45/disk-917719c4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/867492a186ba/vmlinux-917719c4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/61eb606c9dc6/bzImage-917719c4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e5a594...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in ktime_get_ts64 / timekeeping_update_from_shadow

write to 0xffffffff893a7488 of 304 bytes by interrupt on cpu 1:
timekeeping_update_from_shadow+0x40d/0x440 kernel/time/timekeeping.c:829
__timekeeping_advance+0xa5d/0xc10 kernel/time/timekeeping.c:2532
timekeeping_advance kernel/time/timekeeping.c:2540 [inline]
update_wall_time+0x21/0x50 kernel/time/timekeeping.c:2550
tick_do_update_jiffies64+0x169/0x1c0 kernel/time/tick-sched.c:149
tick_sched_do_timer kernel/time/tick-sched.c:253 [inline]
tick_nohz_handler+0x8d/0x3d0 kernel/time/tick-sched.c:312
__run_hrtimer kernel/time/hrtimer.c:1930 [inline]
__hrtimer_run_queues+0x276/0x4f0 kernel/time/hrtimer.c:1994
hrtimer_interrupt+0x261/0x850 kernel/time/hrtimer.c:2113
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
__sysvec_apic_timer_interrupt+0x5f/0x1c0 arch/x86/kernel/apic/apic.c:1067
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
sysvec_apic_timer_interrupt+0x6f/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
start_secondary+0x95/0xa0 arch/x86/kernel/smpboot.c:312
common_startup_64+0x13e/0x147

read to 0xffffffff893a7498 of 8 bytes by task 2982 on cpu 0:
timekeeping_cycles_to_ns kernel/time/timekeeping.c:426 [inline]
timekeeping_get_ns kernel/time/timekeeping.c:449 [inline]
ktime_get_ts64+0xf0/0x350 kernel/time/timekeeping.c:1110
ep_timeout_to_timespec fs/eventpoll.c:1873 [inline]
__do_sys_epoll_wait fs/eventpoll.c:2473 [inline]
__se_sys_epoll_wait fs/eventpoll.c:2467 [inline]
__x64_sys_epoll_wait+0xd9/0x190 fs/eventpoll.c:2467
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/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000f0e113a4a9 -> 0x000000f0e2635616

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2982 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================


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