[moderation] [kernel?] KCSAN: data-race in __mmput / copy_mm (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fcb70a56f4d8 Merge tag 'vfs-6.19-rc8.fixes' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13159a94580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=f7c06a9cf3120d628a4c
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [linux-...@vger.kernel.org lu...@kernel.org pet...@infradead.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/f09fa28d6094/disk-fcb70a56.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d7b2aaa28bcd/vmlinux-fcb70a56.xz
kernel image: https://storage.googleapis.com/syzbot-assets/aa72cf9601a0/bzImage-fcb70a56.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f7c06a...@syzkaller.appspotmail.com

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

write to 0xffff8881b9ec37c0 of 8 bytes by task 16274 on cpu 1:
__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:1178
mmput+0x40/0x50 kernel/fork.c:1196
exit_mm+0xe3/0x180 kernel/exit.c:581
do_exit+0x3fa/0x1590 kernel/exit.c:959
do_group_exit+0xfe/0x140 kernel/exit.c:1112
get_signal+0xe4f/0xf60 kernel/signal.c:3034
arch_do_signal_or_restart+0x96/0x450 arch/x86/kernel/signal.c:337
__exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
exit_to_user_mode_loop+0x6a/0x6f0 kernel/entry/common.c:75
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
do_syscall_64+0x1d3/0x2a0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881b9ec3600 of 1664 bytes by task 10495 on cpu 0:
dup_mm kernel/fork.c:1523 [inline]
copy_mm+0xe1/0x370 kernel/fork.c:1581
copy_process+0xcbd/0x1f10 kernel/fork.c:2221
kernel_clone+0x16b/0x5b0 kernel/fork.c:2651
__do_sys_clone kernel/fork.c:2792 [inline]
__se_sys_clone kernel/fork.c:2776 [inline]
__x64_sys_clone+0x143/0x180 kernel/fork.c:2776
x64_sys_call+0x12d0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:57
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 10495 Comm: syz-executor Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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