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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9f2693489ef8 Merge tag 'scsi-fixes' of git://git.kernel.or..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13fc7c5a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=5aaaa12ad0fefc9b000d
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
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/2447c3f73254/disk-9f269348.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/62bd191e32ba/vmlinux-9f269348.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6ac4ad5ed01e/bzImage-9f269348.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5aaaa1...@syzkaller.appspotmail.com

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

read-write to 0xffff88810476edd0 of 4 bytes by task 14629 on cpu 0:
do_raw_write_seqcount_begin include/linux/seqlock.h:431 [inline]
mm_lock_seqcount_begin include/linux/mmap_lock.h:88 [inline]
mmap_write_lock_killable include/linux/mmap_lock.h:355 [inline]
dup_mmap+0xed/0xf00 mm/mmap.c:1726
dup_mm kernel/fork.c:1529 [inline]
copy_mm+0x119/0x370 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

read to 0xffff88810476ec00 of 1664 bytes by task 14628 on cpu 1:
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: 1 UID: 0 PID: 14628 Comm: syz.4.3331 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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