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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 27fa82620cba Merge tag 'ata-7.1-rc5' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10978ac8580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2e40c0f41e01837e
dashboard link: https://syzkaller.appspot.com/bug?extid=b778b46cbcc31fc2acf0
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [ak...@linux-foundation.org apo...@nvidia.com byun...@sk.com da...@kernel.org gou...@gourry.net joshua...@gmail.com linux-...@vger.kernel.org linu...@kvack.org matthe...@intel.com raki...@sk.com ying....@linux.alibaba.com z...@nvidia.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/dc491bcf1a7c/disk-27fa8262.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f80d7d0085b0/vmlinux-27fa8262.xz
kernel image: https://storage.googleapis.com/syzbot-assets/009aaf28469f/bzImage-27fa8262.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b778b4...@syzkaller.appspotmail.com

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

read-write to 0xffff8881035f52c8 of 4 bytes by task 6571 on cpu 0:
do_raw_write_seqcount_end include/linux/seqlock.h:453 [inline]
mm_lock_seqcount_end include/linux/mmap_lock.h:131 [inline]
vma_end_write_all include/linux/mmap_lock.h:572 [inline]
mmap_write_unlock+0x70/0xc0 include/linux/mmap_lock.h:578
do_mbind mm/mempolicy.c:1611 [inline]
kernel_mbind mm/mempolicy.c:1757 [inline]
__do_sys_mbind mm/mempolicy.c:1831 [inline]
__se_sys_mbind+0xc54/0xdd0 mm/mempolicy.c:1827
__x64_sys_mbind+0x78/0x90 mm/mempolicy.c:1827
x64_sys_call+0x2b72/0x3020 arch/x86/include/generated/asm/syscalls_64.h:238
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881035f5100 of 1664 bytes by task 6574 on cpu 1:
dup_mm kernel/fork.c:1528 [inline]
copy_mm+0xe1/0x370 kernel/fork.c:1586
copy_process+0x1087/0x2370 kernel/fork.c:2264
kernel_clone+0x1a5/0x5e0 kernel/fork.c:2721
__do_sys_clone kernel/fork.c:2862 [inline]
__se_sys_clone kernel/fork.c:2846 [inline]
__x64_sys_clone+0x143/0x180 kernel/fork.c:2846
x64_sys_call+0x1222/0x3020 arch/x86/include/generated/asm/syscalls_64.h:57
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 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: 6574 Comm: syz.3.854 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup