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BUG: KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper

write to 0xffffffff86d4fb88 of 56 bytes by interrupt on cpu 1:
 update_fast_timekeeper+0x38/0x70 kernel/time/timekeeping.c:482
 timekeeping_update_from_shadow+0x3ab/0x440 kernel/time/timekeeping.c:818
 __timekeeping_advance+0xa68/0xc10 kernel/time/timekeeping.c:2614
 timekeeping_advance kernel/time/timekeeping.c:2622 [inline]
 update_wall_time+0x21/0x50 kernel/time/timekeeping.c:2632
 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+0x88/0x380 kernel/time/tick-sched.c:310
 __run_hrtimer kernel/time/hrtimer.c:2032 [inline]
 __hrtimer_run_queues+0x1f8/0x510 kernel/time/hrtimer.c:2096
 hrtimer_interrupt+0x257/0x810 kernel/time/hrtimer.c:2215
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1051 [inline]
 __sysvec_apic_timer_interrupt+0x5f/0x1c0 arch/x86/kernel/apic/apic.c:1068
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0x6f/0x80 arch/x86/kernel/apic/apic.c:1062
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
 native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
 pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:63
 arch_safe_halt arch/x86/kernel/process.c:767 [inline]
 default_idle+0x9/0x20 arch/x86/kernel/process.c:768
 default_idle_call+0x3b/0x60 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:199 [inline]
 do_idle+0x183/0x2d0 kernel/sched/idle.c:355
 cpu_startup_entry+0x24/0x30 kernel/sched/idle.c:454
 start_secondary+0x95/0xa0 arch/x86/kernel/smpboot.c:312
 common_startup_64+0x13e/0x157

read to 0xffffffff86d4fba8 of 8 bytes by task 10199 on cpu 0:
 timekeeping_cycles_to_ns kernel/time/timekeeping.c:450 [inline]
 timekeeping_get_ns kernel/time/timekeeping.c:455 [inline]
 __ktime_get_fast_ns kernel/time/timekeeping.c:503 [inline]
 ktime_get_mono_fast_ns+0xdf/0x1a0 kernel/time/timekeeping.c:543
 ____bpf_ktime_get_ns kernel/bpf/helpers.c:181 [inline]
 bpf_ktime_get_ns+0xe/0x20 kernel/bpf/helpers.c:178
 bpf_prog_b7a80a133741bc4e+0x46/0x4c
 bpf_dispatcher_nop_func include/linux/bpf.h:1454 [inline]
 __bpf_prog_run include/linux/filter.h:724 [inline]
 bpf_prog_run include/linux/filter.h:731 [inline]
 bpf_test_run+0x298/0x620 net/bpf/test_run.c:422
 bpf_prog_test_run_skb+0xe67/0x11b0 net/bpf/test_run.c:1225
 bpf_prog_test_run+0x208/0x340 kernel/bpf/syscall.c:4859
 __sys_bpf+0x8da/0xc30 kernel/bpf/syscall.c:6436
 __do_sys_bpf kernel/bpf/syscall.c:6537 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6534 [inline]
 __x64_sys_bpf+0x69/0x80 kernel/bpf/syscall.c:6534
 x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x002bc8984bd4c2c0 -> 0x002c612ecc042686

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 10199 Comm: syz.0.2082 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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