[syzbot] [kernel?] KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 5200f5f493f7 Linux 7.1-rc4
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11cba536580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2e40c0f41e01837e
dashboard link: https://syzkaller.appspot.com/bug?extid=72789cd1697965e714ca
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f68e006a0a6d/disk-5200f5f4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0eab03c0765f/vmlinux-5200f5f4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9a6094a6b4b6/bzImage-5200f5f4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+72789c...@syzkaller.appspotmail.com

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

write to 0xffffffff893a8488 of 304 bytes by task 5194 on cpu 0:
timekeeping_update_from_shadow+0x40d/0x440 kernel/time/timekeeping.c:829
__timekeeping_inject_offset+0x45c/0x490 kernel/time/timekeeping.c:1661
__do_adjtimex kernel/time/timekeeping.c:2881 [inline]
do_adjtimex+0x390/0x7f0 kernel/time/timekeeping.c:2914
posix_clock_realtime_adj+0x15/0x20 kernel/time/posix-timers.c:207
do_clock_adjtime kernel/time/posix-timers.c:1154 [inline]
__do_sys_clock_adjtime kernel/time/posix-timers.c:1166 [inline]
__se_sys_clock_adjtime kernel/time/posix-timers.c:1157 [inline]
__x64_sys_clock_adjtime+0x145/0x1d0 kernel/time/posix-timers.c:1157
x64_sys_call+0x2794/0x3020 arch/x86/include/generated/asm/syscalls_64.h:306
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

read to 0xffffffff893a84c0 of 8 bytes by task 3377 on cpu 1:
ktime_get_real_seconds+0x15/0x30 kernel/time/timekeeping.c:1156
sched_sync_hw_clock kernel/time/ntp.c:508 [inline]
sync_hw_clock+0x2a8/0x380 kernel/time/ntp.c:665
process_one_work kernel/workqueue.c:3314 [inline]
process_scheduled_works+0x4f0/0x9c0 kernel/workqueue.c:3397
worker_thread+0x58a/0x780 kernel/workqueue.c:3478
kthread+0x22a/0x280 kernel/kthread.c:436
ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x0000000077359b00 -> 0x0000000077359c00

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3377 Comm: kworker/1:3 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: events_freezable_pwr_efficient sync_hw_clock
==================================================================


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