[syzbot] [mm?] kernel BUG in zap_huge_pmd

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4e46774408d9 Merge tag 'for-6.12-rc4-tag' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10fb2ebb980000
kernel config: https://syzkaller.appspot.com/x/.config?x=fc6f8ce8c5369043
dashboard link: https://syzkaller.appspot.com/bug?extid=4b5c704012892c4d22fd
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11f730e7980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=177eae40580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-4e467744.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/058a92aaf61a/vmlinux-4e467744.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0b79757fbe5e/bzImage-4e467744.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4b5c70...@syzkaller.appspotmail.com

R10: 000000000401d031 R11: 0000000000000246 R12: 0000000000000004
R13: 00007f33ed7673fc R14: 00007f33ed737334 R15: 00007f33ed7673e4
</TASK>
------------[ cut here ]------------
kernel BUG at mm/huge_memory.c:2085!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5095 Comm: syz-executor380 Not tainted 6.12.0-rc4-syzkaller-00085-g4e46774408d9 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:zap_huge_pmd+0x953/0xc40 mm/huge_memory.c:2085
Code: fe ff ff f3 0f 1e fa e8 ab 16 92 ff 48 89 df 4c 89 fe e8 50 ba 08 00 e9 2c f8 ff ff e8 96 16 92 ff 90 0f 0b e8 8e 16 92 ff 90 <0f> 0b e8 86 16 92 ff 4c 89 ef 48 c7 c6 20 65 17 8c e8 37 a2 dd ff
RSP: 0018:ffffc9000aeef1e0 EFLAGS: 00010293
RAX: ffffffff8202c152 RBX: 000000000000001e RCX: ffff888000b70000
RDX: 0000000000000000 RSI: 000000000000001f RDI: 000000000000001a
RBP: 000000000000001f R08: ffffffff8202bca6 R09: 1ffff11008416106
R10: dffffc0000000000 R11: ffffed1008416107 R12: 0000000000000000
R13: ffffc9000aeef750 R14: 0000000020e00000 R15: fffffffffffffa00
FS: 000055555711b380(0000) GS:ffff88801fc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055e22940b470 CR3: 000000003daee000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
zap_pmd_range mm/memory.c:1719 [inline]
zap_pud_range mm/memory.c:1768 [inline]
zap_p4d_range mm/memory.c:1789 [inline]
unmap_page_range+0x762/0x40e0 mm/memory.c:1810
unmap_vmas+0x3cc/0x5f0 mm/memory.c:1900
unmap_region+0x214/0x380 mm/vma.c:354
mmap_region+0x23fa/0x2a30 mm/mmap.c:1583
do_mmap+0x8f0/0x1000 mm/mmap.c:496
vm_mmap_pgoff+0x1dd/0x3d0 mm/util.c:588
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f33ed6f19e9
Code: 48 83 c4 28 c3 e8 c7 1b 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc77c44b78 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007ffc77c44be0 RCX: 00007f33ed6f19e9
RDX: 0000000002000007 RSI: 0000000000c00000 RDI: 0000000020400000
RBP: 0000000000000001 R08: 00000000ffffffff R09: 0000000000000000
R10: 000000000401d031 R11: 0000000000000246 R12: 0000000000000004
R13: 00007f33ed7673fc R14: 00007f33ed737334 R15: 00007f33ed7673e4
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:zap_huge_pmd+0x953/0xc40 mm/huge_memory.c:2085
Code: fe ff ff f3 0f 1e fa e8 ab 16 92 ff 48 89 df 4c 89 fe e8 50 ba 08 00 e9 2c f8 ff ff e8 96 16 92 ff 90 0f 0b e8 8e 16 92 ff 90 <0f> 0b e8 86 16 92 ff 4c 89 ef 48 c7 c6 20 65 17 8c e8 37 a2 dd ff
RSP: 0018:ffffc9000aeef1e0 EFLAGS: 00010293
RAX: ffffffff8202c152 RBX: 000000000000001e RCX: ffff888000b70000
RDX: 0000000000000000 RSI: 000000000000001f RDI: 000000000000001a
RBP: 000000000000001f R08: ffffffff8202bca6 R09: 1ffff11008416106
R10: dffffc0000000000 R11: ffffed1008416107 R12: 0000000000000000
R13: ffffc9000aeef750 R14: 0000000020e00000 R15: fffffffffffffa00
FS: 000055555711b380(0000) GS:ffff88801fc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055e22940b470 CR3: 000000003daee000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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 syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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

[Kirill A. Shutemov]

I believe it is bug in mmap_region() around handling
vms_gather_munmap_vmas() and vms_complete_munmap_vmas().

What reproduces does is:

1. Creating hugetlb mapping
2. Setting up UFFD on it
3. Creating a new that partially overlaps with mapping created on step 1

On step 3 an error is injected which makes vma_iter_prealloc() fail and
unmap_region() is called in error path.

The unmap_region() is called with the newly created as an argument, but
page tables still contain entries from hugetlb mapping that was never
fully unmapped because vms_complete_munmap_vmas() has not called yet.

Since the new VMA is not hugetlb, unmapping code takes THP codepath and
calls zap_huge_pmd(). zap_huge_pmd() sees PTE marker swap entry installed
by hugetlb_mfill_atomic_pte() and gets confused.

I don't understand vms_gather/complete_munmap_vmas() code well enough.
I am not sure what the right fix would be.
Maybe call vms_complete_munmap_vmas() earlier?

--
Kiryl Shutsemau / Kirill A. Shutemov

[Lorenzo Stoakes]

We just changed around how this stuff aborts in a hotfix series that should
avoid this, actually.

Unfortunately I don't have the netlink setup syzbot has locally so not sure
how reliably i can repro.

I guess I'll try to tell the bot to try a commit that should work (one that
I'm about to respin, unfortunate timing here...)

[Lorenzo Stoakes]

On Mon, Oct 28, 2024 at 08:31:20PM -0700, syzbot wrote:

> Hello,
>
> syzbot found the following issue on:

Thanks!

This should be resolved with recent changes to rework mmap_region(), let's see...

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/ mm-hotfixes-unstable

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+4b5c70...@syzkaller.appspotmail.com
Tested-by: syzbot+4b5c70...@syzkaller.appspotmail.com

Tested on:

commit: b70a32bb mm/thp: fix deferred split unqueue naming and..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/ mm-hotfixes-unstable
console output: https://syzkaller.appspot.com/x/log.txt?x=155e4a30580000
kernel config: https://syzkaller.appspot.com/x/.config?x=35698c25466f388c

dashboard link: https://syzkaller.appspot.com/bug?extid=4b5c704012892c4d22fd
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.

[Kirill A. Shutemov]

Build the config in the report and run it under KVM (virtme?).

[Lorenzo Stoakes]

No need, syzbot tried the branch with the pending hotfixes and it passes [0]

[0]:https://lore.kernel.org/linux-mm/6720d587.050a022...@google.com/

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.