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KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (4)

Status: upstream: reported on 2026/05/18 12:55
Subsystems: kernel
Labels: race:harmful
[Documentation on labels]
Reported-by: syzbot+72789cd1697965e714ca@syzkaller.appspotmail.com
First crash: 2d18h, last: 2d18h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
7af8d9b4-b6f3-433e-b0e6-f5734a9b6ef3 assessment-kcsan Benign: ❌ KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (4) 2026/05/18 12:23 2026/05/18 12:23 2026/05/18 12:54 55156e845761fb36809c4b3701a920dddce23332
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [kernel?] KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (4) 0 (1) 2026/05/18 12:55
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (2) kernel 6 2 301d 319d 0/29 auto-obsoleted due to no activity on 2025/09/18 01:57
upstream KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (3) kernel 6 2 149d 197d 0/29 auto-obsoleted due to no activity on 2026/02/16 08:50
upstream KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow kernel 6 1 384d 384d 0/29 auto-obsoleted due to no activity on 2025/06/27 01:56

Sample crash report:
==================================================================
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
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/18 12:20 upstream 5200f5f493f7 55156e84 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow
* Struck through repros no longer work on HEAD.