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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:2613
 timekeeping_advance kernel/time/timekeeping.c:2621 [inline]
 update_wall_time+0x21/0x50 kernel/time/timekeeping.c:2631
 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: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+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 25214 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
 ktime_get_boot_fast_ns+0xf/0x40 kernel/time/timekeeping.c:587
 ____bpf_ktime_get_boot_ns kernel/bpf/helpers.c:193 [inline]
 bpf_ktime_get_boot_ns+0xe/0x20 kernel/bpf/helpers.c:190
 bpf_prog_ae25c4385c2fa246+0x28/0x2e
 bpf_dispatcher_xdp_func+0x25/0x30 net/core/filter.c:12022
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run_xdp include/net/xdp.h:696 [inline]
 bpf_test_run+0x22e/0x620 net/bpf/test_run.c:420
 bpf_prog_test_run_xdp+0x587/0x9e0 net/bpf/test_run.c:1469
 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: 0x0005efd7240cd7b0 -> 0x0006886da3e225a8

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 25214 Comm: syz.1.6415 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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