[moderation] [mm?] KCSAN: data-race in __mmput / copy_mm (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 917719c412c4 Merge tag 'selinux-pr-20260507' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17f11696580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2e40c0f41e01837e
dashboard link: https://syzkaller.appspot.com/bug?extid=259d9dfc97438497978a
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [ak...@linux-foundation.org bse...@google.com da...@kernel.org dietmar....@arm.com juri....@redhat.com ke...@kernel.org kpratee...@amd.com li...@infradead.org linux-...@vger.kernel.org linu...@kvack.org l...@kernel.org mgo...@suse.de mho...@suse.com mi...@redhat.com pet...@infradead.org ros...@goodmis.org rp...@kernel.org sur...@google.com vba...@kernel.org vincent...@linaro.org vsch...@redhat.com]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e55e13d50f45/disk-917719c4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/867492a186ba/vmlinux-917719c4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/61eb606c9dc6/bzImage-917719c4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+259d9d...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __mmput / copy_mm

write to 0xffff888103c5e6f8 of 8 bytes by task 20512 on cpu 0:
__list_del include/linux/list.h:203 [inline]
__list_del_entry include/linux/list.h:226 [inline]
list_del include/linux/list.h:237 [inline]
__mmput+0xe2/0x1c0 kernel/fork.c:1183
mmput+0x40/0x50 kernel/fork.c:1201
exit_mm+0x113/0x1a0 kernel/exit.c:581
do_exit+0x442/0x1530 kernel/exit.c:963
do_group_exit+0x138/0x140 kernel/exit.c:1117
__do_sys_exit_group kernel/exit.c:1128 [inline]
__se_sys_exit_group kernel/exit.c:1126 [inline]
__x64_sys_exit_group+0x1f/0x20 kernel/exit.c:1126
x64_sys_call+0x3008/0x3020 arch/x86/include/generated/asm/syscalls_64.h:232
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 0xffff888103c5e540 of 1664 bytes by task 3308 on cpu 1:
dup_mm kernel/fork.c:1528 [inline]
copy_mm+0xe1/0x370 kernel/fork.c:1586
copy_process+0x1087/0x2370 kernel/fork.c:2264
kernel_clone+0x1a5/0x5e0 kernel/fork.c:2721
__do_sys_clone kernel/fork.c:2862 [inline]
__se_sys_clone kernel/fork.c:2846 [inline]
__x64_sys_clone+0x143/0x180 kernel/fork.c:2846
x64_sys_call+0x1222/0x3020 arch/x86/include/generated/asm/syscalls_64.h:57
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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3308 Comm: syz-executor Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================


---
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