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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: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
 preempt_count arch/x86/include/asm/preempt.h:27 [inline]
 get_ctx kernel/kcsan/core.c:206 [inline]
 check_access kernel/kcsan/core.c:750 [inline]
 __tsan_read8+0xbe/0x190 kernel/kcsan/core.c:1025
 iterate_bvec include/linux/iov_iter.h:113 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 __copy_from_iter lib/iov_iter.c:261 [inline]
 copy_folio_from_iter_atomic+0x67f/0x10b0 lib/iov_iter.c:491
 generic_perform_write+0x2c1/0x490 mm/filemap.c:4343
 shmem_file_write_iter+0xc5/0xf0 mm/shmem.c:3478
 __kernel_write_iter+0x319/0x590 fs/read_write.c:621
 dump_emit_page fs/coredump.c:1304 [inline]
 dump_user_range+0xa73/0xd00 fs/coredump.c:1378
 elf_core_dump+0x21a2/0x2330 fs/binfmt_elf.c:2109
 coredump_write+0xacc/0xdd0 fs/coredump.c:1053
 do_coredump fs/coredump.c:1132 [inline]
 vfs_coredump+0x26dd/0x31e0 fs/coredump.c:1206
 get_signal+0xd5c/0xf20 kernel/signal.c:3022
 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 kernel/entry/common.c:98 [inline]
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 irqentry_exit_to_user_mode_prepare include/linux/irq-entry-common.h:252 [inline]
 irqentry_exit_to_user_mode include/linux/irq-entry-common.h:323 [inline]
 irqentry_exit+0x145/0x5d0 kernel/entry/common.c:162
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

read to 0xffffffff86d4fba8 of 8 bytes by task 5419 on cpu 1:
 timekeeping_cycles_to_ns kernel/time/timekeeping.c:444 [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+0xdf/0x1a0 kernel/time/timekeeping.c:537
 ktime_get_boot_fast_ns+0xf/0x40 kernel/time/timekeeping.c:581
 ____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_ae0e084b757e161d+0x4e/0x56
 bpf_dispatcher_nop_func include/linux/bpf.h:1402 [inline]
 __bpf_prog_run include/linux/filter.h:722 [inline]
 bpf_prog_run include/linux/filter.h:729 [inline]
 bpf_test_run+0x29d/0x620 net/bpf/test_run.c:423
 bpf_prog_test_run_skb+0xab1/0x11c0 net/bpf/test_run.c:1192
 bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4742
 __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6266
 __do_sys_bpf kernel/bpf/syscall.c:6361 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6359 [inline]
 __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6359
 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: 0x001f4a618bdf6a42 -> 0x001fe2f80c0ece08

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5419 Comm: syz.3.234 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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