Re: [PULL 52/53] vhost_net: add an assertion for TAP client backends

[Cédric Le Goater]

On 6/28/23 08:45, Ani Sinha wrote:
> > On 28-Jun-2023, at 11:58 AM, Cédric Le Goater <clg@redhat.com> wrote:
> >
> > Hello,
> >
> > On 6/26/23 14:30, Michael S. Tsirkin wrote:
> > > From: Ani Sinha <anisinha@redhat.com>
> > > An assertion was missing for tap vhost backends that enforces a non-null
> > > reference from get_vhost_net(). Both vhost-net-user and vhost-net-vdpa
> > > enforces this. Enforce the same for tap. Unit tests pass with this change.
> > > Signed-off-by: Ani Sinha <anisinha@redhat.com>
> > > Message-Id: <20230619041501.111655-1-anisinha@redhat.com>
> > > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > Reviewed-by: Laurent Vivier <lvivier@redhat.com>
> > > ---
> > >   hw/net/vhost_net.c | 1 +
> > >   1 file changed, 1 insertion(+)
> > > diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> > > index c4eecc6f36..6db23ca323 100644
> > > --- a/hw/net/vhost_net.c
> > > +++ b/hw/net/vhost_net.c
> > > @@ -507,6 +507,7 @@ VHostNetState *get_vhost_net(NetClientState *nc)
> > >       switch (nc->info->type) {
> > >       case NET_CLIENT_DRIVER_TAP:
> > >           vhost_net = tap_get_vhost_net(nc);
> > > +        assert(vhost_net);
> > >           break;
> > >   #ifdef CONFIG_VHOST_NET_USER
> > >       case NET_CLIENT_DRIVER_VHOST_USER:
> >
> > A system of mine without vhost_net (old host kernel) is reaching this assert
>
> We need to understand why this assertion is being hit. It could be a bug 
> somewhere else.

sure.

> What is the backtrace? 


#0  __pthread_kill_implementation (threadid=549621125152, signo=signo@entry=6, 
no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
#1  0x0000007ff71df254 in __pthread_kill_internal (signo=6, threadid=<optimized 
out>) at ./nptl/pthread_kill.c:78
#2  0x0000007ff719a67c in __GI_raise (sig=sig@entry=6) at 
../sysdeps/posix/raise.c:26
#3  0x0000007ff7187130 in __GI_abort () at ./stdlib/abort.c:79
#4  0x0000007ff7193fd0 in __assert_fail_base
    (fmt=0x7ff72ad3f8 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x5556208c00 
"vhost_net", file=file@entry=0x5556208ae0 "../hw/net/vhost_net.c", line=line@entry=510, 
function=function@entry=0x5556208de8 <__PRETTY_FUNCTION__.2> "get_vhost_net") at ./assert/assert.c:92
#5  0x0000007ff7194040 in __GI___assert_fail
    (assertion=assertion@entry=0x5556208c00 "vhost_net", file=file@entry=0x5556208ae0 
"../hw/net/vhost_net.c", line=line@entry=510, function=function@entry=0x5556208de8 
<__PRETTY_FUNCTION__.2> "get_vhost_net") at ./assert/assert.c:101
#6  0x0000005555a767ac in get_vhost_net (nc=<optimized out>) at 
../hw/net/vhost_net.c:510
#7  0x0000005555e6aea8 in virtio_net_get_features (vdev=0x55578cc770, 
features=1105849221095, errp=<optimized out>) at ../hw/net/virtio-net.c:807
#8  0x0000005555b69da4 in virtio_bus_device_plugged 
(vdev=vdev@entry=0x55578cc770, errp=errp@entry=0x7fffffe640) at 
../hw/virtio/virtio-bus.c:66
#9  0x0000005555e8b6a0 in virtio_device_realize (dev=0x55578cc770, 
errp=0x7fffffe6c0) at ../hw/virtio/virtio.c:3609
#10 0x0000005555f1ead8 in device_set_realized (obj=0x55578cc770, value=<optimized 
out>, errp=0x7fffffe898) at ../hw/core/qdev.c:510
#11 0x0000005555f22a14 in property_set_bool (obj=0x55578cc770, v=<optimized out>, 
name=<optimized out>, opaque=0x5556be9ad0, errp=0x7fffffe898) at ../qom/object.c:2285
#12 0x0000005555f260fc in object_property_set (obj=obj@entry=0x55578cc770, 
name=name@entry=0x555621c280 "realized", v=v@entry=0x55578d9310, 
errp=errp@entry=0x7fffffe898)
    at ../qom/object.c:1420
#13 0x0000005555f2a85c in object_property_set_qobject
    (obj=obj@entry=0x55578cc770, name=name@entry=0x555621c280 "realized", 
value=value@entry=0x55578d9250, errp=errp@entry=0x7fffffe898) at ../qom/qom-qobject.c:28
#14 0x0000005555f26820 in object_property_set_bool (obj=0x55578cc770, name=0x555621c280 
"realized", value=<optimized out>, errp=0x7fffffe898) at ../qom/object.c:1489
#15 0x0000005555aafd24 in pci_qdev_realize (qdev=<optimized out>, errp=<optimized 
out>) at ../hw/pci/pci.c:2116
#16 0x0000005555f1ead8 in device_set_realized (obj=0x55578c43a0, value=<optimized 
out>, errp=0x7fffffeae8) at ../hw/core/qdev.c:510
#17 0x0000005555f22a14 in property_set_bool (obj=0x55578c43a0, v=<optimized out>, 
name=<optimized out>, opaque=0x5556be9ad0, errp=0x7fffffeae8) at ../qom/object.c:2285
#18 0x0000005555f260fc in object_property_set (obj=obj@entry=0x55578c43a0, 
name=name@entry=0x555621c280 "realized", v=v@entry=0x55578d34c0, 
errp=errp@entry=0x7fffffeae8)
    at ../qom/object.c:1420
#19 0x0000005555f2a85c in object_property_set_qobject
    (obj=obj@entry=0x55578c43a0, name=name@entry=0x555621c280 "realized", 
value=value@entry=0x55578d3450, errp=errp@entry=0x7fffffeae8) at ../qom/qom-qobject.c:28
#20 0x0000005555f26820 in object_property_set_bool (obj=0x55578c43a0, name=0x555621c280 
"realized", value=<optimized out>, errp=0x7fffffeae8) at ../qom/object.c:1489
#21 0x0000005555ba4f7c in qdev_device_add_from_qdict (opts=opts@entry=0x55578c3110, 
from_json=from_json@entry=false, errp=0x7fffffeae8, errp@entry=0x5556b24a28 
<error_fatal>)
    at ../softmmu/qdev-monitor.c:714
#22 0x0000005555ba5170 in qdev_device_add (opts=0x5556be6060, 
errp=errp@entry=0x5556b24a28 <error_fatal>) at ../softmmu/qdev-monitor.c:733
#23 0x0000005555baa09c in device_init_func (opaque=<optimized out>, opts=<optimized 
out>, errp=0x5556b24a28 <error_fatal>) at ../softmmu/vl.c:1152
#24 0x00000055560b2124 in qemu_opts_foreach
    (list=<optimized out>, func=func@entry=0x5555baa080 <device_init_func>, 
opaque=opaque@entry=0x0, errp=errp@entry=0x5556b24a28 <error_fatal>) at 
../util/qemu-option.c:1135
#25 0x0000005555bac88c in qemu_create_cli_devices () at ../softmmu/vl.c:2573
#26 qmp_x_exit_preconfig (errp=<optimized out>) at ../softmmu/vl.c:2641
#27 0x0000005555bafee4 in qmp_x_exit_preconfig (errp=<optimized out>) at 
../softmmu/vl.c:2635
#28 qemu_init (argc=<optimized out>, argv=<optimized out>) at 
../softmmu/vl.c:3648
#29 0x00000055558e839c in main (argc=<optimized out>, argv=<optimized out>) at 
../softmmu/main.c:47

> What is the repro case?

Nothing special :

qemu-system-aarch64 -M virt -accel kvm -cpu host -nographic -m 2G \
 -drive if=pflash,format=raw,file=./EFI/efi.img,readonly=on \
 -drive if=pflash,format=raw,file=fedora-varstore.img \
 -device virtio-net,netdev=net0,mac=C0:FF:EE:00:00:12,bus=pcie.0,addr=0x3 \
 -netdev 
tap,id=net0,helper=/usr/lib/qemu/qemu-bridge-helper,br=virbr0,vhost=off \
 -drive file=fedora-arm64.qcow2,if=none,id=disk,format=qcow2,cache=none \
 -device virtio-blk-device,drive=disk \
 -serial mon:stdio
qemu-system-aarch64: ../hw/net/vhost_net.c:510: get_vhost_net: Assertion 
`vhost_net' failed.

Thanks,

C.