Re: [PATCH for 7.2-rc? v2 0/5] continuing efforts to fix vhost-user issues

[Alex Bennée]

Alex Bennée <alex.bennee@linaro.org> writes:

> Hi,
>
<snip>
> I can replicate some of the other failures I've been seeing in CI by
> running:
>
>   ../../meson/meson.py test --repeat 10 --print-errorlogs qtest-arm/qos-test
>
> however this seems to run everything in parallel and maybe is better
> at exposing race conditions. Perhaps the CI system makes those races
> easier to hit? Unfortunately I've not been able to figure out exactly
> how things go wrong in the failure case. 
>
<snip>

There is a circular call - we are in vu_gpio_stop which triggers a write
to vhost-user which allows us to catch a disconnect event:

  #0  vhost_dev_is_started (hdev=0x557adf80d878) at 
/home/alex/lsrc/qemu.git/include/hw/virtio/vhost.h:199
  #1  0x0000557adbe0518a in vu_gpio_stop (vdev=0x557adf80d640) at 
../../hw/virtio/vhost-user-gpio.c:138
  #2  0x0000557adbe04d56 in vu_gpio_disconnect (dev=0x557adf80d640) at 
../../hw/virtio/vhost-user-gpio.c:255
  #3  0x0000557adbe049bb in vu_gpio_event (opaque=0x557adf80d640, 
event=CHR_EVENT_CLOSED) at ../../hw/virtio/vhost-user-gpio.c:274
  #4  0x0000557adc0539ef in chr_be_event (s=0x557adea51f10, 
event=CHR_EVENT_CLOSED) at ../../chardev/char.c:61
  #5  0x0000557adc0506aa in qemu_chr_be_event (s=0x557adea51f10, 
event=CHR_EVENT_CLOSED) at ../../chardev/char.c:81
  #6  0x0000557adc04f666 in tcp_chr_disconnect_locked (chr=0x557adea51f10) at 
../../chardev/char-socket.c:470
  #7  0x0000557adc04c81a in tcp_chr_write (chr=0x557adea51f10, 
buf=0x7ffe8588cce0 "\v", len=20) at ../../chardev/char-socket.c:129
  #8  0x0000557adc050999 in qemu_chr_write_buffer (s=0x557adea51f10, 
buf=0x7ffe8588cce0 "\v", len=20, offset=0x7ffe8588cbe4, write_all=true) at 
../../chardev/char.c:121
  #9  0x0000557adc0507c7 in qemu_chr_write (s=0x557adea51f10, 
buf=0x7ffe8588cce0 "\v", len=20, write_all=true) at ../../chardev/char.c:173
  #10 0x0000557adc046f3a in qemu_chr_fe_write_all (be=0x557adf80d830, 
buf=0x7ffe8588cce0 "\v", len=20) at ../../chardev/char-fe.c:53
  #11 0x0000557adbddc02f in vhost_user_write (dev=0x557adf80d878, 
msg=0x7ffe8588cce0, fds=0x0, fd_num=0) at ../../hw/virtio/vhost-user.c:490
  #12 0x0000557adbddd48f in vhost_user_get_vring_base (dev=0x557adf80d878, 
ring=0x7ffe8588d000) at ../../hw/virtio/vhost-user.c:1260
  #13 0x0000557adbdd4bd6 in vhost_virtqueue_stop (dev=0x557adf80d878, 
vdev=0x557adf80d640, vq=0x557adf843570, idx=0) at ../../hw/virtio/vhost.c:1220
  #14 0x0000557adbdd7eda in vhost_dev_stop (hdev=0x557adf80d878, 
vdev=0x557adf80d640, vrings=false) at ../../hw/virtio/vhost.c:1916
  #15 0x0000557adbe051a6 in vu_gpio_stop (vdev=0x557adf80d640) at 
../../hw/virtio/vhost-user-gpio.c:142
  #16 0x0000557adbe04849 in vu_gpio_set_status (vdev=0x557adf80d640, status=15 
'\017') at ../../hw/virtio/vhost-user-gpio.c:173
  #17 0x0000557adbdc87ff in virtio_set_status (vdev=0x557adf80d640, val=15 
'\017') at ../../hw/virtio/virtio.c:2442
  #18 0x0000557adbdcbfa0 in virtio_vmstate_change (opaque=0x557adf80d640, 
running=false, state=RUN_STATE_SHUTDOWN) at ../../hw/virtio/virtio.c:3736
  #19 0x0000557adb91ad27 in vm_state_notify (running=false, 
state=RUN_STATE_SHUTDOWN) at ../../softmmu/runstate.c:334
  #20 0x0000557adb910e88 in do_vm_stop (state=RUN_STATE_SHUTDOWN, 
send_stop=false) at ../../softmmu/cpus.c:262
  #21 0x0000557adb910e30 in vm_shutdown () at ../../softmmu/cpus.c:280
  #22 0x0000557adb91b9c3 in qemu_cleanup () at ../../softmmu/runstate.c:827
  #23 0x0000557adb522975 in qemu_default_main () at ../../softmmu/main.c:38
  #24 0x0000557adb5229a8 in main (argc=27, argv=0x7ffe8588d2f8) at 
../../softmmu/main.c:48
  (rr) p hdev->started
  $9 = true
  (rr) info thread
    Id   Target Id                                Frame 
  * 1    Thread 2140414.2140414 (qemu-system-aar) vhost_dev_is_started 
(hdev=0x557adf80d878) at /home/alex/lsrc/qemu.git/include/hw/virtio/vhost.h:199
    2    Thread 2140414.2140439 (qemu-system-aar) 0x0000000070000002 in 
syscall_traced ()
    3    Thread 2140414.2140442 (qemu-system-aar) 0x0000000070000002 in 
syscall_traced ()
    4    Thread 2140414.2140443 (qemu-system-aar) 0x0000000070000002 in 
syscall_traced ()

During which we eliminate the vhost_dev with a memset:

  Thread 1 hit Hardware watchpoint 2: *(unsigned int *) 0x557adf80da30

  Old value = 2
  New value = 0
  __memset_avx2_unaligned_erms () at 
../sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S:220
  Download failed: Invalid argument.  Continuing without source file 
./string/../sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S.
  220     ../sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S: No such file 
or directory.
  (rr) bt
  #0  __memset_avx2_unaligned_erms () at 
../sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S:220
  #1  0x0000557adbdd67f8 in vhost_dev_cleanup (hdev=0x557adf80d878) at 
../../hw/virtio/vhost.c:1501
  #2  0x0000557adbe04d68 in vu_gpio_disconnect (dev=0x557adf80d640) at 
../../hw/virtio/vhost-user-gpio.c:256
  #3  0x0000557adbe049bb in vu_gpio_event (opaque=0x557adf80d640, 
event=CHR_EVENT_CLOSED) at ../../hw/virtio/vhost-user-gpio.c:274
  #4  0x0000557adc0539ef in chr_be_event (s=0x557adea51f10, 
event=CHR_EVENT_CLOSED) at ../../chardev/char.c:61
  #5  0x0000557adc0506aa in qemu_chr_be_event (s=0x557adea51f10, 
event=CHR_EVENT_CLOSED) at ../../chardev/char.c:81
  #6  0x0000557adc04f666 in tcp_chr_disconnect_locked (chr=0x557adea51f10) at 
../../chardev/char-socket.c:470
  #7  0x0000557adc04c81a in tcp_chr_write (chr=0x557adea51f10, 
buf=0x7ffe8588cce0 "\v", len=20) at ../../chardev/char-socket.c:129
  #8  0x0000557adc050999 in qemu_chr_write_buffer (s=0x557adea51f10, 
buf=0x7ffe8588cce0 "\v", len=20, offset=0x7ffe8588cbe4, write_all=true) at 
../../chardev/char.c:121
  #9  0x0000557adc0507c7 in qemu_chr_write (s=0x557adea51f10, 
buf=0x7ffe8588cce0 "\v", len=20, write_all=true) at ../../chardev/char.c:173
  #10 0x0000557adc046f3a in qemu_chr_fe_write_all (be=0x557adf80d830, 
buf=0x7ffe8588cce0 "\v", len=20) at ../../chardev/char-fe.c:53
  #11 0x0000557adbddc02f in vhost_user_write (dev=0x557adf80d878, 
msg=0x7ffe8588cce0, fds=0x0, fd_num=0) at ../../hw/virtio/vhost-user.c:490
  #12 0x0000557adbddd48f in vhost_user_get_vring_base (dev=0x557adf80d878, 
ring=0x7ffe8588d000) at ../../hw/virtio/vhost-user.c:1260
  #13 0x0000557adbdd4bd6 in vhost_virtqueue_stop (dev=0x557adf80d878, 
vdev=0x557adf80d640, vq=0x557adf843570, idx=0) at ../../hw/virtio/vhost.c:1220
  #14 0x0000557adbdd7eda in vhost_dev_stop (hdev=0x557adf80d878, 
vdev=0x557adf80d640, vrings=false) at ../../hw/virtio/vhost.c:1916
  #15 0x0000557adbe051a6 in vu_gpio_stop (vdev=0x557adf80d640) at 
../../hw/virtio/vhost-user-gpio.c:142
  #16 0x0000557adbe04849 in vu_gpio_set_status (vdev=0x557adf80d640, status=15 
'\017') at ../../hw/virtio/vhost-user-gpio.c:173
  #17 0x0000557adbdc87ff in virtio_set_status (vdev=0x557adf80d640, val=15 
'\017') at ../../hw/virtio/virtio.c:2442
  #18 0x0000557adbdcbfa0 in virtio_vmstate_change (opaque=0x557adf80d640, 
running=false, state=RUN_STATE_SHUTDOWN) at ../../hw/virtio/virtio.c:3736
  #19 0x0000557adb91ad27 in vm_state_notify (running=false, 
state=RUN_STATE_SHUTDOWN) at ../../softmmu/runstate.c:334
  #20 0x0000557adb910e88 in do_vm_stop (state=RUN_STATE_SHUTDOWN, 
send_stop=false) at ../../softmmu/cpus.c:262
  #21 0x0000557adb910e30 in vm_shutdown () at ../../softmmu/cpus.c:280
  #22 0x0000557adb91b9c3 in qemu_cleanup () at ../../softmmu/runstate.c:827
  #23 0x0000557adb522975 in qemu_default_main () at ../../softmmu/main.c:38
  #24 0x0000557adb5229a8 in main (argc=27, argv=0x7ffe8588d2f8) at 
../../softmmu/main.c:48

Before finally:

  #0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
  #1  0x00007f24dc269537 in __GI_abort () at abort.c:79
  #2  0x00007f24dc26940f in __assert_fail_base (fmt=0x7f24dc3e16a8 "%s%s%s:%u: 
%s%sAssertion `%s' failed.\n%n", assertion=0x557adc28d8f5 "assign || nvqs == 
proxy->nvqs_with_notifiers", file=0x557adc28d7ab 
"../../hw/virtio/virtio-pci.c", line=1029, function=<optimized out>) at 
assert.c:92
  #3  0x00007f24dc278662 in __GI___assert_fail (assertion=0x557adc28d8f5 
"assign || nvqs == proxy->nvqs_with_notifiers", file=0x557adc28d7ab 
"../../hw/virtio/virtio-pci.c", line=1029, function=0x557adc28d922 "int 
virtio_pci_set_guest_notifiers(DeviceState *, int, _Bool)") at assert.c:101
  #4  0x0000557adb8e97f1 in virtio_pci_set_guest_notifiers (d=0x557adf805280, 
nvqs=0, assign=false) at ../../hw/virtio/virtio-pci.c:1029
  #5  0x0000557adbe051c7 in vu_gpio_stop (vdev=0x557adf80d640) at 
../../hw/virtio/vhost-user-gpio.c:144
  #6  0x0000557adbe04849 in vu_gpio_set_status (vdev=0x557adf80d640, status=15 
'\017') at ../../hw/virtio/vhost-user-gpio.c:173
  #7  0x0000557adbdc87ff in virtio_set_status (vdev=0x557adf80d640, val=15 
'\017') at ../../hw/virtio/virtio.c:2442
  #8  0x0000557adbdcbfa0 in virtio_vmstate_change (opaque=0x557adf80d640, 
running=false, state=RUN_STATE_SHUTDOWN) at ../../hw/virtio/virtio.c:3736
  #9  0x0000557adb91ad27 in vm_state_notify (running=false, 
state=RUN_STATE_SHUTDOWN) at ../../softmmu/runstate.c:334
  #10 0x0000557adb910e88 in do_vm_stop (state=RUN_STATE_SHUTDOWN, 
send_stop=false) at ../../softmmu/cpus.c:262
  #11 0x0000557adb910e30 in vm_shutdown () at ../../softmmu/cpus.c:280
  #12 0x0000557adb91b9c3 in qemu_cleanup () at ../../softmmu/runstate.c:827
  #13 0x0000557adb522975 in qemu_default_main () at ../../softmmu/main.c:38
  #14 0x0000557adb5229a8 in main (argc=27, argv=0x7ffe8588d2f8) at 
../../softmmu/main.c:48

Because of course we've just done that on disconnect.

Not sure what the cleanest way to avoid that is yet. Maybe it will be
clearer on Monday morning.

-- 
Alex Bennée