[moderation] [mm?] KCSAN: data-race in copy_mm / dup_mmap (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 320475fbd590 Merge tag 'mtd/fixes-for-6.17-rc6' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=114b1934580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6e0c213d0735f5dd
dashboard link: https://syzkaller.appspot.com/bug?extid=e0c8204e48baf95c2067
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/03d005b220b7/disk-320475fb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3ce8904c800d/vmlinux-320475fb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/04e70a318f85/bzImage-320475fb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e0c820...@syzkaller.appspotmail.com

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

read-write to 0xffff888109f473f8 of 4 bytes by task 8792 on cpu 1:
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:417 [inline]
dup_mmap+0xd8/0xf20 mm/mmap.c:1727
dup_mm kernel/fork.c:1485 [inline]
copy_mm+0x11a/0x370 kernel/fork.c:1537
copy_process+0xd08/0x2000 kernel/fork.c:2175
kernel_clone+0x16c/0x5c0 kernel/fork.c:2605
__do_sys_clone kernel/fork.c:2748 [inline]
__se_sys_clone kernel/fork.c:2732 [inline]
__x64_sys_clone+0xe6/0x120 kernel/fork.c:2732
x64_sys_call+0x119c/0x2ff0 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 0xffff888109f47300 of 1408 bytes by task 8791 on cpu 0:
dup_mm kernel/fork.c:1479 [inline]
copy_mm+0xe2/0x370 kernel/fork.c:1537
copy_process+0xd08/0x2000 kernel/fork.c:2175
kernel_clone+0x16c/0x5c0 kernel/fork.c:2605
__do_sys_clone kernel/fork.c:2748 [inline]
__se_sys_clone kernel/fork.c:2732 [inline]
__x64_sys_clone+0xe6/0x120 kernel/fork.c:2732
x64_sys_call+0x119c/0x2ff0 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: 8791 Comm: syz.0.2020 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================
lo speed is unknown, defaulting to 1000
lo speed is unknown, defaulting to 1000


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