Re: WARNING in refcount_sub_and_test

On Fri, Oct 27, 2017 at 12:13 AM, Dmitry Vyukov [off-list ref] wrote:

On Thu, Oct 26, 2017 at 5:49 PM, Xin Long [off-list ref] wrote:

quoted

On Thu, Oct 26, 2017 at 10:49 PM, Dmitry Vyukov [off-list ref] wrote:

quoted

On Thu, Oct 26, 2017 at 10:53 AM, ChunYu Wang [off-list ref] wrote:

quoted

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@localhost

Works, and be able to reproduce the issue. Thanks Dmitry.

Another thing is (you might also notice):
https://paste.fedoraproject.org/paste/N~htmOMPUSiIXGUeLH7yIw
This call trace always comes up after kernel has started.