[syzbot] [mm?] WARNING in hpage_collapse_scan_pmd

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 5eff55d725a4 Merge tag 'platform-drivers-x86-v6.7-7' of gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17472409e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=655f8abe9fe69b3b
dashboard link: https://syzkaller.appspot.com/bug?extid=ed79e0896ae923de13fa
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/496bf4f0c628/disk-5eff55d7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/43482bd7ec93/vmlinux-5eff55d7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fa81d2743202/bzImage-5eff55d7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ed79e0...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 1 PID: 35 at arch/x86/include/asm/pgtable.h:403 pte_uffd_wp arch/x86/include/asm/pgtable.h:403 [inline]
WARNING: CPU: 1 PID: 35 at arch/x86/include/asm/pgtable.h:403 hpage_collapse_scan_pmd+0x233e/0x4fe0 mm/khugepaged.c:1309
Modules linked in:
CPU: 1 PID: 35 Comm: khugepaged Not tainted 6.7.0-rc8-syzkaller-00055-g5eff55d725a4 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
RIP: 0010:pte_uffd_wp arch/x86/include/asm/pgtable.h:403 [inline]
RIP: 0010:hpage_collapse_scan_pmd+0x233e/0x4fe0 mm/khugepaged.c:1309
Code: 24 d8 00 00 00 49 81 c6 00 10 00 00 4c 3b b4 24 f0 00 00 00 0f 83 a8 06 00 00 e8 bd 72 9d ff e9 61 fc ff ff e8 b3 72 9d ff 90 <0f> 0b 90 41 bc 09 00 00 00 45 31 f6 e9 45 f4 ff ff e8 9c 72 9d ff
RSP: 0018:ffffc90000abf780 EFLAGS: 00010293
RAX: ffffffff81f1073d RBX: 0000000000000002 RCX: ffff8880142f1dc0
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
RBP: ffffc90000abfbf0 R08: ffffffff81f0ea47 R09: 1ffffd400022a006
R10: dffffc0000000000 R11: fffff9400022a007 R12: 00000000203ea000
R13: 1ffff92000157f14 R14: 00000000455eac67 R15: 00000000000001ea
FS: 0000000000000000(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f942157a038 CR3: 000000008cd03000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
khugepaged_scan_mm_slot mm/khugepaged.c:2415 [inline]
khugepaged_do_scan mm/khugepaged.c:2503 [inline]
khugepaged+0x9bf/0x17a0 mm/khugepaged.c:2559
kthread+0x2d3/0x370 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
</TASK>


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[Yang Shi]

On Tue, Jan 9, 2024 at 10:23 AM syzbot
<syzbot+ed79e0...@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 5eff55d725a4 Merge tag 'platform-drivers-x86-v6.7-7' of gi..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17472409e80000
> kernel config: https://syzkaller.appspot.com/x/.config?x=655f8abe9fe69b3b
> dashboard link: https://syzkaller.appspot.com/bug?extid=ed79e0896ae923de13fa
> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/496bf4f0c628/disk-5eff55d7.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/43482bd7ec93/vmlinux-5eff55d7.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/fa81d2743202/bzImage-5eff55d7.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+ed79e0...@syzkaller.appspotmail.com
>
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 35 at arch/x86/include/asm/pgtable.h:403 pte_uffd_wp arch/x86/include/asm/pgtable.h:403 [inline]
> WARNING: CPU: 1 PID: 35 at arch/x86/include/asm/pgtable.h:403 hpage_collapse_scan_pmd+0x233e/0x4fe0 mm/khugepaged.c:1309
> Modules linked in:
> CPU: 1 PID: 35 Comm: khugepaged Not tainted 6.7.0-rc8-syzkaller-00055-g5eff55d725a4 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> RIP: 0010:pte_uffd_wp arch/x86/include/asm/pgtable.h:403 [inline]

Khugepaged saw a uffd wp PTE is writable. Khugepaged just scans the
page table at this stage, so it sounds like something is out of sync?

Cc'ed Peter.

[Peter Xu]

Thanks for copying me, Yang.

Currently I have no clue of what is going wrong. I'll need to have a
closer look some day later on the rest logs, or wait for a reproducer with
some more information.

--
Peter Xu

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.