[moderation] [mm?] KCSAN: data-race in copy_mm / dup_mmap

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8c6bc74c7f89 Merge tag 'v6.16-rc1-smb3-client-fixes' of gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14b8090c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=75ba7d6bc4eb7c9d
dashboard link: https://syzkaller.appspot.com/bug?extid=24c50dcbbd8b8aa29990
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [Liam.H...@oracle.com ak...@linux-foundation.org ja...@google.com linux-...@vger.kernel.org linu...@kvack.org lorenzo...@oracle.com pfal...@suse.de vba...@suse.cz]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8bb8ff23b86b/disk-8c6bc74c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b8ce1c10350a/vmlinux-8c6bc74c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/eff1a0604096/bzImage-8c6bc74c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+24c50d...@syzkaller.appspotmail.com

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

read-write to 0xffff88811a5645f8 of 4 bytes by task 11225 on cpu 1:
do_raw_write_seqcount_begin include/linux/seqlock.h:431 [inline]
mm_lock_seqcount_begin include/linux/mmap_lock.h:87 [inline]
mmap_write_lock_killable include/linux/mmap_lock.h:376 [inline]
dup_mmap+0xd8/0xf20 mm/mmap.c:1731
dup_mm kernel/fork.c:1477 [inline]
copy_mm+0x11a/0x370 kernel/fork.c:1529
copy_process+0xcf1/0x1fe0 kernel/fork.c:2169
kernel_clone+0x16c/0x5b0 kernel/fork.c:2599
__do_sys_clone kernel/fork.c:2742 [inline]
__se_sys_clone kernel/fork.c:2726 [inline]
__x64_sys_clone+0xe6/0x120 kernel/fork.c:2726
x64_sys_call+0x2c59/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:57
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a564500 of 1408 bytes by task 11223 on cpu 0:
dup_mm kernel/fork.c:1471 [inline]
copy_mm+0xe2/0x370 kernel/fork.c:1529
copy_process+0xcf1/0x1fe0 kernel/fork.c:2169
kernel_clone+0x16c/0x5b0 kernel/fork.c:2599
__do_sys_clone kernel/fork.c:2742 [inline]
__se_sys_clone kernel/fork.c:2726 [inline]
__x64_sys_clone+0xe6/0x120 kernel/fork.c:2726
x64_sys_call+0x2c59/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:57
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 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: 11223 Comm: syz.0.2412 Not tainted 6.16.0-rc1-syzkaller-00236-g8c6bc74c7f89 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.