[Bug 1888601] Re: QEMU v5.1.0-rc0/rc1 hang with nested virtualization

[Dr. David Alan Gilbert]

If even with that fix it's failing =and giving a similar back trace,
then:

Thread 4 (LWP 23729):
#0 0x00007f9ae5fed337 in __strcmp_sse2 ()
#1 0x00007f9ae5d9a8ad in g_str_equal () at pthread_create.c:679
#2 0x00007f9ae5d99a9d in g_hash_table_lookup () at pthread_create.c:679
#3 0x00007f9ae5ac728f in type_table_lookup (name=0x7f9ae609c9dd "virtio-bus") 
at qom/object.c:84
#4 type_get_by_name (name=0x7f9ae609c9dd "virtio-bus") at qom/object.c:171
#5 object_class_dynamic_cast (class=class@entry=0x5555572d1ac0, 
typename=typename@entry=0x7f9ae609c9dd "virtio-bus") at qom/object.c:879

seems weird to me - why would you be stuck in a g_str_equal for any length of 
time (yet 2 of your backtraces both have it); yet the filename and symbol name 
don't really look like they're matching so I'm suspicious.
Have you got a minimal non-kata way to reproduce this?

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https://bugs.launchpad.net/bugs/1888601

Title:
  QEMU v5.1.0-rc0/rc1 hang with nested virtualization

Status in QEMU:
  New

Bug description:
  We're running Kata Containers using QEMU and with v5.1.0rc0 and rc1
  have noticed a problem at startup where QEMu appears to hang. We are
  not seeing this problem on our bare metal nodes and only on a VSI that
  supports nested virtualization.

  We unfortunately see nothing at all in the QEMU logs to help
  understand the problem and a hung process is just a guess at this
  point.

  Using git bisect we first see the problem with...

  ---

  f19bcdfedd53ee93412d535a842a89fa27cae7f2 is the first bad commit
  commit f19bcdfedd53ee93412d535a842a89fa27cae7f2
  Author: Jason Wang <jasowang@redhat.com>
  Date:   Wed Jul 1 22:55:28 2020 +0800

      virtio-pci: implement queue_enabled method

      With version 1, we can detect whether a queue is enabled via
      queue_enabled.

      Signed-off-by: Jason Wang <jasowang@redhat.com>
      Signed-off-by: Cindy Lu <lulu@redhat.com>
      Message-Id: <20200701145538.22333-5-lulu@redhat.com>
      Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
      Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
      Acked-by: Jason Wang <jasowang@redhat.com>

   hw/virtio/virtio-pci.c | 13 +++++++++++++
   1 file changed, 13 insertions(+)

  ---

  Reverting this commit (on top of 5.1.0-rc1) seems to work and prevent
  the hanging.

  ---

  Here's how kata ends up launching qemu in our environment --
  /opt/kata/bin/qemu-system-x86_64 -name 
sandbox-849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f -uuid 
6bec458e-1da7-4847-a5d7-5ab31d4d2465 -machine pc,accel=kvm,kernel_irqchip -cpu 
host,pmu=off -qmp 
unix:/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/qmp.sock,server,nowait
 -m 4096M,slots=10,maxmem=30978M -device 
pci-bridge,bus=pci.0,id=pci-bridge-0,chassis_nr=1,shpc=on,addr=2,romfile= 
-device virtio-serial-pci,disable-modern=true,id=serial0,romfile= -device 
virtconsole,chardev=charconsole0,id=console0 -chardev 
socket,id=charconsole0,path=/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/console.sock,server,nowait
 -device virtio-scsi-pci,id=scsi0,disable-modern=true,romfile= -object 
rng-random,id=rng0,filename=/dev/urandom -device 
virtio-rng-pci,rng=rng0,romfile= -device 
virtserialport,chardev=charch0,id=channel0,name=agent.channel.0 -chardev 
socket,id=charch0,path=/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/kata.sock,server,nowait
 -chardev 
socket,id=char-396c5c3e19e29353,path=/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/vhost-fs.sock
 -device 
vhost-user-fs-pci,chardev=char-396c5c3e19e29353,tag=kataShared,romfile= -netdev 
tap,id=network-0,vhost=on,vhostfds=3:4,fds=5:6 -device 
driver=virtio-net-pci,netdev=network-0,mac=52:ac:2d:02:1f:6f,disable-modern=true,mq=on,vectors=6,romfile=
 -global kvm-pit.lost_tick_policy=discard -vga none -no-user-config -nodefaults 
-nographic -daemonize -object 
memory-backend-file,id=dimm1,size=4096M,mem-path=/dev/shm,share=on -numa 
node,memdev=dimm1 -kernel /opt/kata/share/kata-containers/vmlinuz-5.7.9-74 
-initrd 
/opt/kata/share/kata-containers/kata-containers-initrd_alpine_1.11.2-6_agent.initrd
 -append tsc=reliable no_timer_check rcupdate.rcu_expedited=1 i8042.direct=1 
i8042.dumbkbd=1 i8042.nopnp=1 i8042.noaux=1 noreplace-smp reboot=k console=hvc0 
console=hvc1 iommu=off cryptomgr.notests net.ifnames=0 pci=lastbus=0 debug 
panic=1 nr_cpus=4 agent.use_vsock=false scsi_mod.scan=none 
init=/usr/bin/kata-agent -pidfile 
/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/pid 
-D 
/run/vc/vm/849df14c6065931adedb9d18bc9260a6d896f1814a8c5cfa239865772f1b7a5f/qemu.log
 -smp 2,cores=1,threads=1,sockets=4,maxcpus=4

  ---

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