Re: [PATCH] virtio-serial-bus: do cleanup on the error path in realize() to avoid memleaks

[Markus Armbruster <armbru@redhat.com>]

Pan Nengyuan <pannengyuan@huawei.com> writes:

> port->bh forgot to delete on the error path, this patch add it to fix memleaks. It's easy to reproduce as follow(add a same nr port):
>     {'execute': 'device_add', 'arguments': {'id': 'virtio_serial_pci0', 'driver': 'virtio-serial-pci', 'bus': 'pci.0', 'addr': '0x5'}, 'id': 'yVkZcGgV'}
>     {'execute': 'device_add', 'arguments': {'id': 'port1', 'driver': 'virtserialport', 'name': 'port1', 'chardev': 'channel1', 'bus': 'virtio_serial_pci0.0', 'nr': 1}, 'id': '3dXdUgJA'}
>     {'execute': 'device_add', 'arguments': {'id': 'port2', 'driver': 'virtserialport', 'name': 'port2', 'chardev': 'channel2', 'bus': 'virtio_serial_pci0.0', 'nr': 1}, 'id': 'qLzcCkob'}
>     {'execute': 'device_add', 'arguments': {'id': 'port2', 'driver': 'virtserialport', 'name': 'port2', 'chardev': 'channel2', 'bus': 'virtio_serial_pci0.0', 'nr': 2}, 'id': 'qLzcCkob'}
>
> The leak stack:
> Direct leak of 40 byte(s) in 1 object(s) allocated from:
>     #0 0x7f04a8008ae8 in __interceptor_malloc (/lib64/libasan.so.5+0xefae8)
>     #1 0x7f04a73cf1d5 in g_malloc (/lib64/libglib-2.0.so.0+0x531d5)
>     #2 0x56273eaee484 in aio_bh_new /mnt/sdb/backup/qemu/util/async.c:125
>     #3 0x56273eafe9a8 in qemu_bh_new /mnt/sdb/backup/qemu/util/main-loop.c:532
>     #4 0x56273d52e62e in virtser_port_device_realize /mnt/sdb/backup/qemu/hw/char/virtio-serial-bus.c:946
>     #5 0x56273dcc5040 in device_set_realized /mnt/sdb/backup/qemu/hw/core/qdev.c:891
>     #6 0x56273e5ebbce in property_set_bool /mnt/sdb/backup/qemu/qom/object.c:2238
>     #7 0x56273e5e5a9c in object_property_set /mnt/sdb/backup/qemu/qom/object.c:1324
>     #8 0x56273e5ef5f8 in object_property_set_qobject /mnt/sdb/backup/qemu/qom/qom-qobject.c:26
>     #9 0x56273e5e5e6a in object_property_set_bool /mnt/sdb/backup/qemu/qom/object.c:1390
>     #10 0x56273daa40de in qdev_device_add /mnt/sdb/backup/qemu/qdev-monitor.c:680
>     #11 0x56273daa53e9 in qmp_device_add /mnt/sdb/backup/qemu/qdev-monitor.c:805
>
> Reported-by: Euler Robot <euler.robot@huawei.com>
> Signed-off-by: Pan Nengyuan <pannengyuan@huawei.com>

Fixes: 199646d81522509ac2dba6d28c31e8c7d807bc93

> ---
>  hw/char/virtio-serial-bus.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
> index 941ed5aca9..563b845f71 100644
> --- a/hw/char/virtio-serial-bus.c
> +++ b/hw/char/virtio-serial-bus.c
> @@ -957,13 +957,13 @@ static void virtser_port_device_realize(DeviceState *dev, Error **errp)
>      if (find_port_by_id(port->vser, port->id)) {
>          error_setg(errp, "virtio-serial-bus: A port already exists at id %u",
>                     port->id);
> -        return;
> +        goto fail;
>      }
>  
>      if (port->name != NULL && find_port_by_name(port->name)) {
>          error_setg(errp, "virtio-serial-bus: A port already exists by name %s",
>                     port->name);
> -        return;
> +        goto fail;
>      }
>  
>      if (port->id == VIRTIO_CONSOLE_BAD_ID) {
> @@ -974,7 +974,7 @@ static void virtser_port_device_realize(DeviceState *dev, Error **errp)
>              if (port->id == VIRTIO_CONSOLE_BAD_ID) {
>                  error_setg(errp, "virtio-serial-bus: Maximum port limit for "
>                                   "this device reached");
> -                return;
> +                goto fail;
>              }
>          }
>      }
> @@ -983,16 +983,20 @@ static void virtser_port_device_realize(DeviceState *dev, Error **errp)
>      if (port->id >= max_nr_ports) {
>          error_setg(errp, "virtio-serial-bus: Out-of-range port id specified, "
>                           "max. allowed: %u", max_nr_ports - 1);
> -        return;
> +        goto fail;
>      }
>  
>      vsc->realize(dev, &err);
>      if (err != NULL) {
>          error_propagate(errp, err);
> -        return;
> +        goto fail;
>      }
>  
>      port->elem = NULL;
> +    return;
> +
> +fail:
> +    qemu_bh_delete(port->bh);
>  }
>  
>  static void virtser_port_device_plug(HotplugHandler *hotplug_dev,

Looks correct to me.

However, I wonder whether we could simply create port->bh later.  It's
for use by virtio_serial_throttle_port(), called on incoming migration
via virtio_serial_load_device(), virtio_load(), virtio_device_get().  It
runs flush_queued_data(), which does nothing unless
virtio_queue_ready(port->ovq).

Note that virtio_queue_ready() dereferences its argument.  It's safe
only after virtser_port_device_plug() set port->ovq.  I'd expect that to
be possible only while the device is realized.  If that's correct, we
could simply create port->bh last in virtser_port_device_realize().