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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 0:
 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
 kcsan_setup_watchpoint+0x3e8/0x450 kernel/kcsan/core.c:705
 scm_set_cred include/net/scm.h:73 [inline]
 unix_skb_to_scm net/unix/af_unix.c:2000 [inline]
 __unix_dgram_recvmsg+0x5c2/0x860 net/unix/af_unix.c:2633
 unix_dgram_recvmsg+0x7e/0x90 net/unix/af_unix.c:2681
 sock_recvmsg_nosec+0xc2/0xf0 net/socket.c:1126
 ____sys_recvmsg+0x26f/0x280 net/socket.c:2902
 ___sys_recvmsg+0x11f/0x3a0 net/socket.c:2946
 do_recvmmsg+0x1e5/0x560 net/socket.c:3041
 __sys_recvmmsg net/socket.c:3115 [inline]
 __do_sys_recvmmsg net/socket.c:3138 [inline]
 __se_sys_recvmmsg net/socket.c:3131 [inline]
 __x64_sys_recvmmsg+0xe5/0x170 net/socket.c:3131
 x64_sys_call+0x80f/0x3020 arch/x86/include/generated/asm/syscalls_64.h:300
 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

read to 0xffffffff86d4fba8 of 8 bytes by task 6327 on cpu 1:
 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_e4c647e6fd0061e8+0x20/0x26
 bpf_dispatcher_nop_func include/linux/bpf.h:1454 [inline]
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run include/linux/filter.h:730 [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: 0x000505b010823b68 -> 0x0005946b200830e1

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 6327 Comm: syz.2.839 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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