KCSAN: data-race in copy_mm / lru_gen_del_mm (3)

Status: upstream: reported on 2026/09/21 01:03
Subsystems: mm
Labels: prio:low race:harmful
[Documentation on labels]
Reported-by: syzbot+c6e1b1b32ff2fc3b7d60@syzkaller.appspotmail.com
First crash: 2d03h, last: 2d03h
▶ ▼ ✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision
fa90a9de assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KCSAN: data-race in copy_mm / lru_gen_del_mm (3) 2026/09/21 00:02 2026/09/21 00:02 2026/09/21 00:46 853b104b
ac24de7e assessment-kcsan Benign: ❌ ❓ KCSAN: data-race in copy_mm / lru_gen_del_mm (3) 2026/09/21 00:02 2026/09/21 00:02 2026/09/21 01:02 853b104b
5f05a71a assessment-kcsan 💥 KCSAN: data-race in copy_mm / lru_gen_del_mm (3) 2026/09/19 01:55 2026/09/19 01:55 2026/09/19 03:15 853b104b
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [mm?] KCSAN: data-race in copy_mm / lru_gen_del_mm (3) 0 (1) 2026/09/21 01:03
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in copy_mm / lru_gen_del_mm mm 6 4 198d 245d 0/29 auto-obsoleted due to no activity on 2026/05/01 15:24
upstream KCSAN: data-race in copy_mm / lru_gen_del_mm (2) race:benign prio:low mm 6 1 64d 64d 0/29 auto-obsoleted due to no activity on 2026/09/12 18:50

Sample crash report:
==================================================================
BUG: KCSAN: data-race in copy_mm / lru_gen_del_mm

write to 0xffff8881077eb088 of 8 bytes by task 7336 on cpu 0:
 __list_del include/linux/list.h:241 [inline]
 __list_del_entry include/linux/list.h:264 [inline]
 list_del_init include/linux/list.h:333 [inline]
 lru_gen_del_mm+0x299/0x3e0 mm/vmscan.c:2998
 __mmput+0x17a/0x1c0 kernel/fork.c:1203
 mmput+0x40/0x50 kernel/fork.c:1216
 exit_mm+0x113/0x1a0 kernel/exit.c:617
 do_exit+0x438/0x1510 kernel/exit.c:999
 do_group_exit+0x138/0x140 kernel/exit.c:1154
 __do_sys_exit_group kernel/exit.c:1165 [inline]
 __se_sys_exit_group kernel/exit.c:1163 [inline]
 __x64_sys_exit_group+0x1f/0x20 kernel/exit.c:1163
 x64_sys_call+0x254f/0x2550 arch/x86/include/generated/asm/syscalls_64.h:232
 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 0xffff8881077eaa00 of 1728 bytes by task 7337 on cpu 1:
 dup_mm kernel/fork.c:1537 [inline]
 copy_mm+0xd6/0x340 kernel/fork.c:1595
 copy_process+0x10ad/0x2340 kernel/fork.c:2310
 kernel_clone+0x1c0/0x5f0 kernel/fork.c:2769
 __do_sys_clone kernel/fork.c:2911 [inline]
 __se_sys_clone kernel/fork.c:2895 [inline]
 __x64_sys_clone+0x143/0x180 kernel/fork.c:2895
 x64_sys_call+0x2479/0x2550 arch/x86/include/generated/asm/syscalls_64.h:57
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 7337 Comm: dhcpcd-run-hook Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/19 01:36 upstream 17e7b8eacf4c 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_mm / lru_gen_del_mm
* Struck through repros no longer work on HEAD.