[moderation] [kernel?] KCSAN: data-race in ktime_get_coarse_real_ts64 / timekeeping_update_from_shadow
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syzbot
May 31, 2026, 12:59:29 PM (yesterday) May 31
to syzkaller-upst...@googlegroups.com
Hello,
syzbot found the following issue on:
HEAD commit: 174914ea5513 Merge tag 'v7.1-rc6-smb3-client-fixes' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15c297a6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f571f22917457cd8
dashboard link: https://syzkaller.appspot.com/bug?extid=e730469cb55c88acd2a7
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
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/6b4c7364c9bf/disk-174914ea.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d35079434152/vmlinux-174914ea.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ba7aef805464/bzImage-174914ea.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e73046...@syzkaller.appspotmail.com
==================================================================
BUG: KCSAN: data-race in ktime_get_coarse_real_ts64 / timekeeping_update_from_shadow
write to 0xffffffff893ae488 of 304 bytes by interrupt on cpu 0:
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
kcsan_setup_watchpoint+0x404/0x410 kernel/kcsan/core.c:705
lowmem_page_address include/linux/mm.h:2973 [inline]
folio_address include/linux/mm.h:2984 [inline]
slab_address mm/slab.h:153 [inline]
obj_to_index mm/slab.h:305 [inline]
__memcg_slab_free_hook+0x99/0x2c0 mm/memcontrol.c:3528
memcg_slab_free_hook mm/slub.c:2488 [inline]
slab_free mm/slub.c:6248 [inline]
kfree+0x291/0x370 mm/slub.c:6566
skb_kfree_head net/core/skbuff.c:1075 [inline]
skb_free_head+0x53/0x220 net/core/skbuff.c:1087
skb_release_data+0x5c4/0x600 net/core/skbuff.c:1114
skb_release_all net/core/skbuff.c:1189 [inline]
__kfree_skb+0x44/0x150 net/core/skbuff.c:1203
consume_skb+0x4b/0x130 net/core/skbuff.c:1436
skb_free_datagram+0x15/0x20 net/core/datagram.c:324
__unix_dgram_recvmsg+0x784/0x870 net/unix/af_unix.c:2669
unix_dgram_recvmsg+0x7e/0x90 net/unix/af_unix.c:2686
sock_recvmsg_nosec net/socket.c:1137 [inline]
sock_recvmsg+0xf5/0x120 net/socket.c:1159
sock_read_iter+0x169/0x1b0 net/socket.c:1229
new_sync_read fs/read_write.c:493 [inline]
vfs_read+0x6c0/0x7f0 fs/read_write.c:574
ksys_read+0xdc/0x1a0 fs/read_write.c:717
__do_sys_read fs/read_write.c:726 [inline]
__se_sys_read fs/read_write.c:724 [inline]
__x64_sys_read+0x40/0x50 fs/read_write.c:724
x64_sys_call+0x2886/0x3020 arch/x86/include/generated/asm/syscalls_64.h:1
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 0xffffffff893ae4f8 of 4 bytes by task 3023 on cpu 1:
tk_xtime_coarse kernel/time/timekeeping.c:212 [inline]
ktime_get_coarse_real_ts64+0x6b/0xf0 kernel/time/timekeeping.c:2583
audit_get_stamp kernel/audit.c:1892 [inline]
audit_log_start+0x5b7/0x730 kernel/audit.c:1970
common_lsm_audit+0x65/0x230 security/lsm_audit.c:442
slow_avc_audit+0x14c/0x190 security/selinux/avc.c:779
avc_audit security/selinux/include/avc.h:131 [inline]
avc_has_perm+0x144/0x190 security/selinux/avc.c:1198
sock_has_perm security/selinux/hooks.c:4928 [inline]
selinux_socket_recvmsg+0x1ab/0x1e0 security/selinux/hooks.c:5275
security_socket_recvmsg+0x4c/0x90 security/security.c:4330
sock_recvmsg+0x38/0x120 net/socket.c:1157
____sys_recvmsg+0xf5/0x280 net/socket.c:2918
___sys_recvmsg+0x11f/0x3b0 net/socket.c:2960
__sys_recvmsg net/socket.c:2993 [inline]
__do_sys_recvmsg net/socket.c:2999 [inline]
__se_sys_recvmsg net/socket.c:2996 [inline]
__x64_sys_recvmsg+0xd1/0x160 net/socket.c:2996
x64_sys_call+0x2b1a/0x3020 arch/x86/include/generated/asm/syscalls_64.h:48
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: 0x1c09ccd9 -> 0x1c9887ea
Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3023 Comm: dhcpcd Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================
audit: audit_backlog=65 > audit_backlog_limit=64
audit: audit_lost=1327 audit_rate_limit=0 audit_backlog_limit=64
audit: backlog limit exceeded
audit: audit_backlog=65 > audit_backlog_limit=64
audit: audit_lost=1328 audit_rate_limit=0 audit_backlog_limit=64
audit: audit_backlog=65 > audit_backlog_limit=64
audit: audit_lost=1537 audit_rate_limit=0 audit_backlog_limit=64
audit: backlog limit exceeded
audit: audit_backlog=65 > audit_backlog_limit=64
audit: audit_lost=1538 audit_rate_limit=0 audit_backlog_limit=64
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
syzbot found the following issue on:
HEAD commit: 174914ea5513 Merge tag 'v7.1-rc6-smb3-client-fixes' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15c297a6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f571f22917457cd8
dashboard link: https://syzkaller.appspot.com/bug?extid=e730469cb55c88acd2a7
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
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/6b4c7364c9bf/disk-174914ea.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d35079434152/vmlinux-174914ea.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ba7aef805464/bzImage-174914ea.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e73046...@syzkaller.appspotmail.com
==================================================================
BUG: KCSAN: data-race in ktime_get_coarse_real_ts64 / timekeeping_update_from_shadow
write to 0xffffffff893ae488 of 304 bytes by interrupt on cpu 0:
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
kcsan_setup_watchpoint+0x404/0x410 kernel/kcsan/core.c:705
lowmem_page_address include/linux/mm.h:2973 [inline]
folio_address include/linux/mm.h:2984 [inline]
slab_address mm/slab.h:153 [inline]
obj_to_index mm/slab.h:305 [inline]
__memcg_slab_free_hook+0x99/0x2c0 mm/memcontrol.c:3528
memcg_slab_free_hook mm/slub.c:2488 [inline]
slab_free mm/slub.c:6248 [inline]
kfree+0x291/0x370 mm/slub.c:6566
skb_kfree_head net/core/skbuff.c:1075 [inline]
skb_free_head+0x53/0x220 net/core/skbuff.c:1087
skb_release_data+0x5c4/0x600 net/core/skbuff.c:1114
skb_release_all net/core/skbuff.c:1189 [inline]
__kfree_skb+0x44/0x150 net/core/skbuff.c:1203
consume_skb+0x4b/0x130 net/core/skbuff.c:1436
skb_free_datagram+0x15/0x20 net/core/datagram.c:324
__unix_dgram_recvmsg+0x784/0x870 net/unix/af_unix.c:2669
unix_dgram_recvmsg+0x7e/0x90 net/unix/af_unix.c:2686
sock_recvmsg_nosec net/socket.c:1137 [inline]
sock_recvmsg+0xf5/0x120 net/socket.c:1159
sock_read_iter+0x169/0x1b0 net/socket.c:1229
new_sync_read fs/read_write.c:493 [inline]
vfs_read+0x6c0/0x7f0 fs/read_write.c:574
ksys_read+0xdc/0x1a0 fs/read_write.c:717
__do_sys_read fs/read_write.c:726 [inline]
__se_sys_read fs/read_write.c:724 [inline]
__x64_sys_read+0x40/0x50 fs/read_write.c:724
x64_sys_call+0x2886/0x3020 arch/x86/include/generated/asm/syscalls_64.h:1
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 0xffffffff893ae4f8 of 4 bytes by task 3023 on cpu 1:
tk_xtime_coarse kernel/time/timekeeping.c:212 [inline]
ktime_get_coarse_real_ts64+0x6b/0xf0 kernel/time/timekeeping.c:2583
audit_get_stamp kernel/audit.c:1892 [inline]
audit_log_start+0x5b7/0x730 kernel/audit.c:1970
common_lsm_audit+0x65/0x230 security/lsm_audit.c:442
slow_avc_audit+0x14c/0x190 security/selinux/avc.c:779
avc_audit security/selinux/include/avc.h:131 [inline]
avc_has_perm+0x144/0x190 security/selinux/avc.c:1198
sock_has_perm security/selinux/hooks.c:4928 [inline]
selinux_socket_recvmsg+0x1ab/0x1e0 security/selinux/hooks.c:5275
security_socket_recvmsg+0x4c/0x90 security/security.c:4330
sock_recvmsg+0x38/0x120 net/socket.c:1157
____sys_recvmsg+0xf5/0x280 net/socket.c:2918
___sys_recvmsg+0x11f/0x3b0 net/socket.c:2960
__sys_recvmsg net/socket.c:2993 [inline]
__do_sys_recvmsg net/socket.c:2999 [inline]
__se_sys_recvmsg net/socket.c:2996 [inline]
__x64_sys_recvmsg+0xd1/0x160 net/socket.c:2996
x64_sys_call+0x2b1a/0x3020 arch/x86/include/generated/asm/syscalls_64.h:48
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: 0x1c09ccd9 -> 0x1c9887ea
Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3023 Comm: dhcpcd Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================
audit: audit_backlog=65 > audit_backlog_limit=64
audit: audit_lost=1327 audit_rate_limit=0 audit_backlog_limit=64
audit: backlog limit exceeded
audit: audit_backlog=65 > audit_backlog_limit=64
audit: audit_lost=1328 audit_rate_limit=0 audit_backlog_limit=64
audit: audit_backlog=65 > audit_backlog_limit=64
audit: audit_lost=1537 audit_rate_limit=0 audit_backlog_limit=64
audit: backlog limit exceeded
audit: audit_backlog=65 > audit_backlog_limit=64
audit: audit_lost=1538 audit_rate_limit=0 audit_backlog_limit=64
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
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