[syzbot] [kernel?] KCSAN: data-race in __mmput / copy_mm (4)

[syzbot] [kernel?] KCSAN: data-race in __mmput / copy_mm (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    fe2ec83746e5 Merge tag 'hid-for-linus-2026092202' of git:/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13895405580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ea1e6d8de13bab08
dashboard link: https://syzkaller.appspot.com/bug?extid=a4bf7413d2424fa6e235
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8d62b1e87101/disk-fe2ec837.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f842c0393d08/vmlinux-fe2ec837.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b8e7137bfc1e/bzImage-fe2ec837.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a4bf7413d2424fa6e235@syzkaller.appspotmail.com

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

write to 0xffff8881046681f8 of 8 bytes by task 21217 on cpu 1:
 __list_del include/linux/list.h:241 [inline]
 __list_del_entry include/linux/list.h:264 [inline]
 list_del include/linux/list.h:275 [inline]
 __mmput+0xe2/0x1c0 kernel/fork.c:1198
 mmput+0x40/0x50 kernel/fork.c:1216
 exit_mm+0x113/0x1a0 kernel/exit.c:618
 do_exit+0x438/0x1510 kernel/exit.c:1000
 do_group_exit+0xfe/0x140 kernel/exit.c:1155
 get_signal+0xe07/0xf10 kernel/signal.c:3112
 arch_do_signal_or_restart+0x96/0x480 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
 exit_to_user_mode_loop+0x15d/0x8c0 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:343 [inline]
 do_syscall_64+0x212/0x360 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888104668000 of 1728 bytes by task 3876 on cpu 0:
 dup_mm kernel/fork.c:1537 [inline]
 copy_mm+0xd6/0x340 kernel/fork.c:1595
 copy_process+0x108a/0x2350 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: 0 UID: 0 PID: 3876 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
==================================================================


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