Stefan Hajnoczi <stefa...@gmail.com> writes:
> On Sat, 26 Nov 2022 at 04:45, Alex Bennée <alex.ben...@linaro.org> wrote:
>>
>>
>> Alex Bennée <alex.ben...@linaro.org> writes:
>>
>> > Alex Bennée <alex.ben...@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
>>
>> I suspect the best choice here is to schedule the cleanup as a later
>> date. Should I use the aio_bh one shots for this or maybe an rcu cleanup
>> event?
>>
>> Paolo, any suggestions?
>>
>> > #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
>
> Does this mean the backend closed the connection before receiving all
> the vhost-user protocol messages sent by QEMU?
>
> This looks like a backend bug. It prevents QEMU's vhost-user client
> from cleanly stopping the virtqueue (vhost_virtqueue_stop()).
Well the backend in this case is the qtest framework so not the worlds
most complete implementation.
> QEMU is still broken if it cannot handle disconnect at any time. Maybe
> a simple solution for that is to check for reentrancy (either by
> checking an existing variable or adding a new one to prevent
> vu_gpio_stop() from calling itself).
vhost-user-blk introduced an additional flag:
/*
* There are at least two steps of initialization of the
* vhost-user device. The first is a "connect" step and
* second is a "start" step. Make a separation between
* those initialization phases by using two fields.
*/
/* vhost_user_blk_connect/vhost_user_blk_disconnect */
bool connected;
/* vhost_user_blk_start/vhost_user_blk_stop */
bool started_vu;
but that in itself is not enough. If you look at the various cases of
handling CHR_EVENT_CLOSED you'll see some schedule the shutdown with aio
and some don't even bother (so will probably break the same way).
Rather than have a mish-mash of solutions maybe we should introduce a
new vhost function - vhost_user_async_close() which can take care of the
scheduling and wrap it with a check for a valid vhost structure in case
it gets shutdown in the meantime?
>
>> > #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
>>
--
Alex Bennée
