KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper

Status: moderation: reported on 2026/04/26 15:09
Subsystems: kernel
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+86d8f93cf23743800fc8@syzkaller.appspotmail.com
First crash: 148d, last: 1d06h
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
0cc79473 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ✅ VMHostTrigger: ❌ KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper 2026/05/12 03:02 2026/05/12 03:02 2026/05/12 03:47 d168f260
e59ce648 assessment-kcsan Benign: ✅ Confident: ✅ KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper 2026/04/26 15:09 2026/04/26 15:09 2026/04/26 15:29 9c2d0995

Sample crash report:
==================================================================
BUG: KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper

write to 0xffffffff86f4fd48 of 56 bytes by interrupt on cpu 0:
 update_fast_timekeeper+0x38/0x70 kernel/time/timekeeping.c:509
 timekeeping_update_from_shadow+0x3c0/0x480 kernel/time/timekeeping.c:845
 __timekeeping_advance+0xb36/0xcf0 kernel/time/timekeeping.c:2663
 timekeeping_advance kernel/time/timekeeping.c:2671 [inline]
 update_wall_time+0x21/0x50 kernel/time/timekeeping.c:2681
 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:2074 [inline]
 __hrtimer_run_queues+0x1f8/0x510 kernel/time/hrtimer.c:2131
 hrtimer_interrupt+0x27b/0x860 kernel/time/hrtimer.c:2250
 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
 arch_atomic64_read arch/x86/include/asm/atomic64_64.h:15 [inline]
 raw_atomic64_read include/linux/atomic/atomic-arch-fallback.h:2583 [inline]
 raw_atomic_long_read include/linux/atomic/atomic-long.h:38 [inline]
 atomic_long_read include/linux/atomic/atomic-instrumented.h:3189 [inline]
 find_watchpoint kernel/kcsan/core.c:131 [inline]
 check_access kernel/kcsan/core.c:745 [inline]
 __tsan_read1+0x28/0x180 kernel/kcsan/core.c:1030
 __skb_datagram_iter+0x185/0x680 net/core/datagram.c:415
 skb_copy_datagram_iter+0x3f/0xf0 net/core/datagram.c:535
 skb_copy_datagram_msg include/linux/skbuff.h:4273 [inline]
 __unix_dgram_recvmsg+0x4a8/0x860 net/unix/af_unix.c:2632
 unix_dgram_recvmsg+0x7e/0x90 net/unix/af_unix.c:2689
 sock_recvmsg_nosec+0xc2/0xf0 net/socket.c:1151
 ____sys_recvmsg+0x26f/0x280 net/socket.c:2931
 ___sys_recvmsg+0x11f/0x3a0 net/socket.c:2975
 do_recvmmsg+0x1e5/0x560 net/socket.c:3070
 __sys_recvmmsg net/socket.c:3144 [inline]
 __do_sys_recvmmsg net/socket.c:3167 [inline]
 __se_sys_recvmmsg net/socket.c:3160 [inline]
 __x64_sys_recvmmsg+0xe5/0x170 net/socket.c:3160
 x64_sys_call+0x77f/0x2550 arch/x86/include/generated/asm/syscalls_64.h:300
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff86f4fd58 of 8 bytes by task 1008 on cpu 1:
 timekeeping_cycles_to_ns kernel/time/timekeeping.c:459 [inline]
 timekeeping_get_ns kernel/time/timekeeping.c:482 [inline]
 __ktime_get_fast_ns kernel/time/timekeeping.c:530 [inline]
 ktime_get_mono_fast_ns+0x92/0x1a0 kernel/time/timekeeping.c:570
 pm_runtime_mark_last_busy include/linux/pm_runtime.h:235 [inline]
 usb_mark_last_busy include/linux/usb.h:823 [inline]
 usb_autopm_put_interface+0x29/0x60 drivers/usb/core/driver.c:1796
 hub_event+0x299e/0x2aa0 drivers/usb/core/hub.c:6008
 process_one_work kernel/workqueue.c:3396 [inline]
 process_scheduled_works+0x56a/0xa50 kernel/workqueue.c:3479
 worker_thread+0x569/0x750 kernel/workqueue.c:3560
 kthread+0x223/0x270 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: 0x00000029872681c3 -> 0x0000002988763bda

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 1008 Comm: kworker/1:2 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: usb_hub_wq hub_event
==================================================================

Crashes (25):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/21 03:50 upstream 518e5b794c06 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/09/14 08:03 upstream 704340f1cd0d 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/09/07 08:10 upstream 88405f0ad1d5 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/09/06 09:16 upstream 1fc5a74b108f 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/09/03 08:53 upstream 940de590b839 6a988719 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/08/31 07:29 upstream cee9395acd80 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/08/30 17:33 upstream 08dbfad3f504 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/08/09 19:16 upstream 06cf61899d64 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/08/07 06:08 upstream f9a2394a2348 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/07/17 07:49 upstream fce2dfa773ce 7f27c57a .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/07/07 15:15 upstream 0e35b9b6ec0f 76cdc0c0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/06/29 16:29 upstream dc59e4fea9d8 6a0c72dc .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/06/27 12:58 upstream 5a66900afbd6 fb92f11c .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/06/26 00:09 upstream a142da0b2d32 7ff32d8b .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/06/21 04:27 upstream 1a3746ccbb0a 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/06/17 17:31 upstream 66affa37cfac b62b3ded .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/06/17 17:30 upstream 66affa37cfac b62b3ded .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/06/14 06:14 upstream 2b07ea76fd28 1d2f3589 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/05/31 18:12 upstream 174914ea5513 6b4a8443 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/05/28 00:48 upstream eb3f4b7426cf 4c36e7e5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/05/17 16:06 upstream 6916d5703ddf de5aae85 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/05/13 01:43 upstream c21b90f77687 a0949470 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/05/10 16:20 upstream 1bfaee9d3351 29233ece .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/05/09 07:19 upstream 27a26ccfd528 29233ece .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
2026/04/26 15:09 upstream 897d54018cc9 9c2d0995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_mono_fast_ns / update_fast_timekeeper
* Struck through repros no longer work on HEAD.