Re: [syzbot] [erofs?] WARNING: CPU: NUM PID: NUM at mm/page_alloc.c:LINE get_page_from_freeli

From: Xiang Gao <hsiangkao@linux.alibaba.com>
To: Aleksandr Nogikh <nogikh@google.com>
Cc: syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org,
	akpm@linux-foundation.org, linux-erofs@lists.ozlabs.org,
	syzbot <syzbot+c3729cda01706a04fb98@syzkaller.appspotmail.com>
Subject: Re: [syzbot] [erofs?] WARNING: CPU: NUM PID: NUM at mm/page_alloc.c:LINE get_page_from_freeli
Date: Thu, 5 Jan 2023 23:59:08 +0800	[thread overview]
Message-ID: <03ada837-2504-9e69-5fec-0b7a7f186d90@linux.alibaba.com> (raw)
In-Reply-To: <CANp29Y63rCdepVtantxdJEcvbRv0D61gfY_oGV7dgrmEGgPdLw@mail.gmail.com>

Hi Aleksandr,

On 2023/1/5 19:14, Aleksandr Nogikh wrote:
> Hi,
> 
> On Thu, Jan 5, 2023 at 11:54 AM Xiang Gao <hsiangkao@linux.alibaba.com> wrote:
> 
>> I wasn't able to build the kernel with this kernel config, it shows:
>> "...
>> FATAL: modpost: vmlinux.o is truncated. sechdrs[i].sh_offset=1399394064 > sizeof(*hrd)=64
>> make[2]: *** [Module.symvers] Error 1
>> make[1]: *** [modpost] Error 2
>> make: *** [__sub-make] Error 2
>> "
> 
> Could you please tell, what exact compiler/linker version did you use?

Thanks for your help.

GCC 9.2.1 on my developping server.

> 
> 
>>>
>>> Downloadable assets:
>>> disk image: https://storage.googleapis.com/syzbot-assets/0c8a5f06ceb3/disk-f9ff5644.raw.xz
>>> vmlinux: https://storage.googleapis.com/syzbot-assets/be222e852ae2/vmlinux-f9ff5644.xz
>>> kernel image: https://storage.googleapis.com/syzbot-assets/d9f42a53b05e/bzImage-f9ff5644.xz
>>
>> Finally I tried the original kernel image, and it printed some other
>> random bug when booting system and then reboot, like:
>>
>> [   36.991123][    T1] ==================================================================
>> [   36.991800][    T1] BUG: KASAN: slab-out-of-bounds in copy_array+0x96/0x100
>> [   36.992438][    T1] Write of size 32 at addr ffff888018c34640 by task systemd/1
> < .. >
> 
> Interesting!
> I've just tried to boot it with qemu and it was fine.
> 
> qemu-system-x86_64 -smp 2,sockets=2,cores=1 -m 4G -drive
> file=disk-f9ff5644.raw,format=raw -snapshot -nographic -enable-kvm
> 
> So it looks like it's some difference between these VMMs that causes
> that bug to fire.

I think the problem is that the rootfs which I used has more complicated
workload than the given one.

> 
>>
>> May I ask it can be reproducable on the latest -rc kernel?
> 
> We can ask syzbot about v6.2-rc2:
> 
> #syz test git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
> 88603b6dc419445847923fcb7fe5080067a30f98

I think I know the root cause: It seems that kvcalloc doesn't support
GFP_NOFAIL, I will use kcalloc directly instead.

Thanks,
Gao Xiang

> 
>>
>> Thanks,
>> Gao Xiang
>>
> 
> --
> Aleksandr