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BUG: KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper

write to 0xffffffff86d4fb48 of 56 bytes by interrupt on cpu 0:
 update_fast_timekeeper+0x38/0x70 kernel/time/timekeeping.c:476
 timekeeping_update_from_shadow+0x3ab/0x440 kernel/time/timekeeping.c:812
 __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
 kcsan_setup_watchpoint+0x404/0x410 kernel/kcsan/core.c:705
 folios_put_refs+0x4e/0x2d0 mm/swap.c:963
 free_pages_and_swap_cache+0x2af/0x3a0 mm/swap_state.c:401
 __tlb_batch_free_encoded_pages mm/mmu_gather.c:138 [inline]
 tlb_batch_pages_flush mm/mmu_gather.c:151 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:417 [inline]
 tlb_flush_mmu+0x557/0x6d0 mm/mmu_gather.c:424
 zap_pte_range mm/memory.c:1973 [inline]
 zap_pmd_range mm/memory.c:2020 [inline]
 zap_pud_range mm/memory.c:2048 [inline]
 zap_p4d_range mm/memory.c:2069 [inline]
 __zap_vma_range+0x24b9/0x2c20 mm/memory.c:2109
 unmap_vmas+0x22a/0x340 mm/memory.c:2178
 exit_mmap+0x1ab/0x5f0 mm/mmap.c:1300
 __mmput+0x28/0x1c0 kernel/fork.c:1178
 mmput+0x40/0x50 kernel/fork.c:1201
 exit_mm+0x15f/0x1f0 kernel/exit.c:582
 do_exit+0x442/0x1530 kernel/exit.c:964
 do_group_exit+0xfe/0x140 kernel/exit.c:1119
 get_signal+0xe30/0xf20 kernel/signal.c:3037
 arch_do_signal_or_restart+0x96/0x480 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0x6f/0x820 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
 do_syscall_64+0x232/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86d4fb58 of 8 bytes by task 8898 on cpu 1:
 timekeeping_cycles_to_ns kernel/time/timekeeping.c:426 [inline]
 timekeeping_get_ns kernel/time/timekeeping.c:449 [inline]
 __ktime_get_fast_ns kernel/time/timekeeping.c:497 [inline]
 ktime_get_mono_fast_ns+0x92/0x1a0 kernel/time/timekeeping.c:537
 ____bpf_ktime_get_ns kernel/bpf/helpers.c:181 [inline]
 bpf_ktime_get_ns+0xe/0x20 kernel/bpf/helpers.c:178
 bpf_prog_b1adb4c1a433d624+0x23/0x29
 bpf_dispatcher_xdp_func+0x25/0x30 net/core/filter.c:11940
 __bpf_prog_run include/linux/filter.h:722 [inline]
 bpf_prog_run_xdp include/net/xdp.h:696 [inline]
 bpf_test_run+0x233/0x620 net/bpf/test_run.c:421
 bpf_prog_test_run_xdp+0x5a9/0xa10 net/bpf/test_run.c:1432
 bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4742
 __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6292
 __do_sys_bpf kernel/bpf/syscall.c:6387 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6385 [inline]
 __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6385
 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+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000dc428aa111 -> 0x000000dc43da527e

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 8898 Comm: syz.3.1417 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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