[moderation] [kernel?] KCSAN: data-race in ktime_get_coarse_ts64 / timekeeping_update_from_shadow (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 51512e22efe8 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15ca8951580000
kernel config: https://syzkaller.appspot.com/x/.config?x=84b3039e8461eef5
dashboard link: https://syzkaller.appspot.com/bug?extid=106d69e9dc1822a52985
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
CC: [jst...@google.com linux-...@vger.kernel.org sb...@kernel.org tg...@kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/412eaa5aa52e/disk-51512e22.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/36b6c4e7cef2/vmlinux-51512e22.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c026a5294394/bzImage-51512e22.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+106d69...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in ktime_get_coarse_ts64 / timekeeping_update_from_shadow

write to 0xffffffff893d04c8 of 304 bytes by interrupt on cpu 0:
timekeeping_update_from_shadow+0x40d/0x440 kernel/time/timekeeping.c:835
__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
rest_init+0xee/0xf0 init/main.c:717
start_kernel+0x49f/0x4d0 init/main.c:1175
x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
x86_64_start_kernel+0xfc/0x100 arch/x86/kernel/head64.c:291
common_startup_64+0x13e/0x157

read to 0xffffffff893d0538 of 4 bytes by task 27175 on cpu 1:
tk_xtime_coarse kernel/time/timekeeping.c:217 [inline]
ktime_get_coarse_ts64+0x6d/0x120 kernel/time/timekeeping.c:2767
ktime_get_coarse include/linux/timekeeping.h:133 [inline]
ktime_get_coarse_ns include/linux/timekeeping.h:139 [inline]
____bpf_ktime_get_coarse_ns kernel/bpf/helpers.c:204 [inline]
bpf_ktime_get_coarse_ns+0x39/0xb0 kernel/bpf/helpers.c:202
bpf_prog_ce3dfd7f9330a559+0x1e/0x29
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_prog_run_pin_on_cpu include/linux/filter.h:748 [inline]
bpf_flow_dissect+0x14f/0x340 net/core/flow_dissector.c:1024
bpf_prog_test_run_flow_dissector+0x25d/0x360 net/bpf/test_run.c:1558
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: 0x12a4ed7a -> 0x133d83fa

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 27175 Comm: syz.7.5461 Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================


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