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KCSAN: data-race in ktime_get_coarse_real_ts64_mg / timekeeping_update_from_shadow

Status: moderation: reported on 2026/04/21 11:15
Subsystems: kernel
[Documentation on labels]
Reported-by: syzbot+a1d9ae81eab6ce5f53dd@syzkaller.appspotmail.com
First crash: 18d, last: 11d
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
57d5c7f4-61f8-48bd-83ff-7047f425d85c assessment-kcsan Benign: ✅ Confident: ✅ KCSAN: data-race in ktime_get_coarse_real_ts64_mg / timekeeping_update_from_shadow 2026/04/21 11:15 2026/04/21 11:15 2026/04/21 11:33 3f2e655b2741ba770abc65f58ac94b7e897edae8

Sample crash report:
==================================================================
BUG: KCSAN: data-race in ktime_get_coarse_real_ts64_mg / timekeeping_update_from_shadow

write to 0xffffffff893a4488 of 304 bytes by interrupt on cpu 1:
 timekeeping_update_from_shadow+0x40d/0x440 kernel/time/timekeeping.c:829
 __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
 __sanitizer_cov_trace_pc+0x45/0x70 kernel/kcov.c:222
 __copy_msghdr net/socket.c:2599 [inline]
 copy_msghdr_from_user net/socket.c:2631 [inline]
 recvmsg_copy_msghdr net/socket.c:2884 [inline]
 ___sys_recvmsg+0x2d6/0x3b0 net/socket.c:2956
 do_recvmmsg+0x1ef/0x560 net/socket.c:3055
 __sys_recvmmsg net/socket.c:3129 [inline]
 __do_sys_recvmmsg net/socket.c:3152 [inline]
 __se_sys_recvmmsg net/socket.c:3145 [inline]
 __x64_sys_recvmmsg+0xe5/0x170 net/socket.c:3145
 x64_sys_call+0x80f/0x3020 arch/x86/include/generated/asm/syscalls_64.h:300
 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 0xffffffff893a44f8 of 4 bytes by task 2984 on cpu 0:
 tk_xtime_coarse kernel/time/timekeeping.c:212 [inline]
 ktime_get_coarse_real_ts64_mg+0x89/0x1a0 kernel/time/timekeeping.c:2606
 current_time+0x41/0x240 fs/inode.c:2370
 inode_update_atime fs/inode.c:2093 [inline]
 inode_update_time fs/inode.c:2156 [inline]
 generic_update_time fs/inode.c:2189 [inline]
 touch_atime+0x17b/0x330 fs/inode.c:2267
 do_readlinkat+0x137/0x2f0 fs/stat.c:582
 __do_sys_readlink fs/stat.c:605 [inline]
 __se_sys_readlink fs/stat.c:602 [inline]
 __x64_sys_readlink+0x47/0x60 fs/stat.c:602
 x64_sys_call+0x2b51/0x3020 arch/x86/include/generated/asm/syscalls_64.h:90
 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: 0x39db5eff -> 0x3a740907

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2984 Comm: udevd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/29 01:04 upstream dca922e019dd 95008c03 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_coarse_real_ts64_mg / timekeeping_update_from_shadow
2026/04/21 11:15 upstream b4e07588e743 3f2e655b .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_coarse_real_ts64_mg / timekeeping_update_from_shadow
* Struck through repros no longer work on HEAD.