linux-kernel - Re: WARNING in refcount_sub_and

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Message-ID: <CACT4Y+YegVs8c75nJ5caFPiz8wctj_7n-C3F=RC5PVE1R2uDOQ@mail.gmail.com>
Date:   Thu, 26 Oct 2017 18:13:51 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     ChunYu Wang <chunwang@...hat.com>,
        syzbot 
        <bot+a004c8dcbae7c160bf1bbd6e6af2e9cf4fa54f84@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>, linux-sctp@...r.kernel.org,
        netdev <netdev@...r.kernel.org>,
        Neil Horman <nhorman@...driver.com>,
        syzkaller-bugs@...glegroups.com,
        Vladislav Yasevich <vyasevich@...il.com>
Subject: Re: WARNING in refcount_sub_and_test

On Thu, Oct 26, 2017 at 5:49 PM, Xin Long <lucien.xin@...il.com> wrote:
> On Thu, Oct 26, 2017 at 10:49 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> On Thu, Oct 26, 2017 at 10:53 AM, ChunYu Wang <chunwang@...hat.com> wrote:
>>> Hi all,
>>>
>>> I am failed to reproduce it on target kernel with the reproducer file
>>> or replaying the target syzkaller description log file, do I made
>>> something wrong or there exists more subjects then the line in
>>> repro.txt:
>>>
>>> #{Threaded:true Collide:true Repeat:false Procs:1 Sandbox:namespace
>>> Fault:false FaultCall:-1 FaultNth:0 EnableTun:false UseTmpDir:true
>>> HandleSegv:false WaitRepeat:false Debug:false Repro:false}
>>
>>
>> Hi ChunYu,
>>
>> I've just re-tested the C repro and was able to trigger the bug in a second.
>> I've checked out 49ca1943a7adb429b11b8e05d81bc821694b76c7, copied the
>> provided config, run make olddefconfig, built with gcc-7 (you can get
>> the exact one here
>> https://storage.googleapis.com/syzkaller/gcc-7.tar.gz). Then run in
>> qemu (most of the flags are probably irrelevant):
>>
>> qemu-system-x86_64 -hda wheezy.img -net
>> user,host=10.0.2.10,hostfwd=tcp::10022-:22 -net nic -nographic -kernel
>> arch/x86/boot/bzImage -append "kvm-intel.nested=1
>> kvm-intel.unrestricted_guest=1 kvm-intel.ept=1
>> kvm-intel.flexpriority=1 kvm-intel.vpid=1
>> kvm-intel.emulate_invalid_guest_state=1 kvm-intel.eptad=1
>> kvm-intel.enable_shadow_vmcs=1 kvm-intel.pml=1
>> kvm-intel.enable_apicv=1 console=ttyS0 root=/dev/sda
>> earlyprintk=serial slub_debug=UZ vsyscall=native rodata=n oops=panic
>> panic_on_warn=1 panic=86400" -enable-kvm -pidfile vm_pid -m 2G -smp 4
>> -cpu host -usb -usbdevice mouse -usbdevice tablet -soundhw all
> Just wondering where we can get wheezy.img, if I can't download
> somewhere, can you provide one if possible ?
>
> I made some imgs before, with kernel built with the .config mail-list
> usually gave, the guest always failed to boot.

Makes sense. Added image/key links here:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#crash-does-not-reproduce

Here are commands to start qemu, ssh into the VM. This just worked for
me to reproduce the crash.

qemu-system-x86_64 -hda wheezy.img -net
user,host=10.0.2.10,hostfwd=tcp::10022-:22 -net nic -nographic -kernel
arch/x86/boot/bzImage -append "kvm-intel.nested=1
kvm-intel.unrestricted_guest=1 kvm-intel.ept=1
kvm-intel.flexpriority=1 kvm-intel.vpid=1
kvm-intel.emulate_invalid_guest_state=1 kvm-intel.eptad=1
kvm-intel.enable_shadow_vmcs=1 kvm-intel.pml=1
kvm-intel.enable_apicv=1 console=ttyS0 root=/dev/sda
earlyprintk=serial vsyscall=native rodata=n oops=panic panic_on_warn=1
panic=86400" -enable-kvm -m 2G -smp 4 -cpu host -usb -usbdevice mouse
-usbdevice tablet -soundhw all

ssh -i wheezy.img.key -p 10022 -o UserKnownHostsFile=/dev/null -o
StrictHostKeyChecking=no -o IdentitiesOnly=yes root@...alhost