[moderation] [mm?] KCSAN: data-race in __anon_vma_prepare / __vmf_anon_prepare

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 07d9df80082b Merge tag 'perf-tools-fixes-for-v6.17-2025-08..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=119cbc62580000
kernel config: https://syzkaller.appspot.com/x/.config?x=86a2212b48ce4ce2
dashboard link: https://syzkaller.appspot.com/bug?extid=7fbe71f971ba56626d82
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
CC: [Liam.H...@oracle.com ak...@linux-foundation.org da...@redhat.com harr...@oracle.com linux-...@vger.kernel.org linu...@kvack.org lorenzo...@oracle.com ri...@surriel.com vba...@suse.cz]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4d171f55c84c/disk-07d9df80.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a98c7e116e81/vmlinux-07d9df80.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7681910e0d3d/bzImage-07d9df80.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7fbe71...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __anon_vma_prepare / __vmf_anon_prepare

write to 0xffff88811a78b700 of 8 bytes by task 5708 on cpu 1:
__anon_vma_prepare+0x172/0x2f0 mm/rmap.c:213
__vmf_anon_prepare+0x91/0x100 mm/memory.c:3506
hugetlb_no_page mm/hugetlb.c:6471 [inline]
hugetlb_fault+0x770/0x1b50 mm/hugetlb.c:6725
handle_mm_fault+0x1861/0x2c20 mm/memory.c:6362
faultin_page mm/gup.c:1144 [inline]
__get_user_pages+0x102e/0x1fa0 mm/gup.c:1446
populate_vma_page_range mm/gup.c:1880 [inline]
__mm_populate+0x243/0x3a0 mm/gup.c:1983
mm_populate include/linux/mm.h:3367 [inline]
vm_mmap_pgoff+0x232/0x2e0 mm/util.c:585
ksys_mmap_pgoff+0x2d0/0x310 mm/mmap.c:604
x64_sys_call+0x14a3/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:10
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 0xffff88811a78b700 of 8 bytes by task 5707 on cpu 0:
__vmf_anon_prepare+0x26/0x100 mm/memory.c:3500
hugetlb_no_page mm/hugetlb.c:6471 [inline]
hugetlb_fault+0x770/0x1b50 mm/hugetlb.c:6725
handle_mm_fault+0x1861/0x2c20 mm/memory.c:6362
do_user_addr_fault+0x3fe/0x1090 arch/x86/mm/fault.c:1387
handle_page_fault arch/x86/mm/fault.c:1476 [inline]
exc_page_fault+0x62/0xa0 arch/x86/mm/fault.c:1532
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
rep_movs_alternative+0x4a/0x90 arch/x86/lib/copy_user_64.S:68
copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
raw_copy_to_user arch/x86/include/asm/uaccess_64.h:147 [inline]
copy_to_user_iter lib/iov_iter.c:25 [inline]
iterate_ubuf include/linux/iov_iter.h:30 [inline]
iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
_copy_to_iter+0x141/0xe70 lib/iov_iter.c:185
copy_to_iter include/linux/uio.h:220 [inline]
simple_copy_to_iter net/core/datagram.c:521 [inline]
__skb_datagram_iter+0xc6/0x690 net/core/datagram.c:402
skb_copy_datagram_iter+0x3d/0x110 net/core/datagram.c:535
skb_copy_datagram_msg include/linux/skbuff.h:4167 [inline]
unix_stream_read_actor+0x43/0x70 net/unix/af_unix.c:3135
unix_stream_read_generic+0x6b1/0x1580 net/unix/af_unix.c:3058
unix_stream_recvmsg+0xc3/0xf0 net/unix/af_unix.c:3172
sock_recvmsg_nosec net/socket.c:1065 [inline]
sock_recvmsg+0x136/0x170 net/socket.c:1087
____sys_recvmsg+0xf5/0x280 net/socket.c:2834
___sys_recvmsg+0x11f/0x370 net/socket.c:2876
__sys_recvmsg net/socket.c:2909 [inline]
__do_sys_recvmsg net/socket.c:2915 [inline]
__se_sys_recvmsg net/socket.c:2912 [inline]
__x64_sys_recvmsg+0xd1/0x160 net/socket.c:2912
x64_sys_call+0x2b42/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:48
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

value changed: 0x0000000000000000 -> 0xffff8881270b8d68

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 5707 Comm: syz.6.491 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================


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[Dmitry Vyukov]

#syz set race: harmful

LLM says so...

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[syzbot]

Sending this report to the next reporting stage.