On Wed, Apr 04, 2012 at 12:32:29PM +0300, Michael S. Tsirkin wrote: > On Thu, Dec 29, 2011 at 09:12:38PM +1030, Rusty Russell wrote: > > Michael S. Tsirkin noticed that we could run the refill work after > > ndo_close, which can re-enable napi - we don't disable it until > > virtnet_remove. This is clearly wrong, so move the workqueue control > > to ndo_open and ndo_stop (aka. virtnet_open and virtnet_close). > > > > One subtle point: virtnet_probe() could simply fail if it couldn't > > allocate a receive buffer, but that's less polite in virtnet_open() so > > we schedule a refill as we do in the normal receive path if we run out > > of memory. > > > > Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx> > > Doh. > napi_disable does not prevent the following > napi_schedule, does it? > > Can someone confirm that I am not seeing things please? Yes, I *was* seeing things. After napi_disable, NAPI_STATE_SCHED is set to napi_schedule does nothing. Sorry about the noise. > And this means this hack does not work: > try_fill_recv can still run in parallel with > napi, corrupting the vq. > > I suspect we need to resurrect a patch that used a > dedicated flag to avoid this race. > > Comments? > > > --- > > drivers/net/virtio_net.c | 17 +++++++++++++---- > > 1 file changed, 13 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -439,7 +439,13 @@ static int add_recvbuf_mergeable(struct > > return err; > > } > > > > -/* Returns false if we couldn't fill entirely (OOM). */ > > +/* > > + * Returns false if we couldn't fill entirely (OOM). > > + * > > + * Normally run in the receive path, but can also be run from ndo_open > > + * before we're receiving packets, or from refill_work which is > > + * careful to disable receiving (using napi_disable). > > + */ > > static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp) > > { > > int err; > > @@ -719,6 +725,10 @@ static int virtnet_open(struct net_devic > > { > > struct virtnet_info *vi = netdev_priv(dev); > > > > + /* Make sure we have some buffers: if oom use wq. */ > > + if (!try_fill_recv(vi, GFP_KERNEL)) > > + schedule_delayed_work(&vi->refill, 0); > > + > > virtnet_napi_enable(vi); > > return 0; > > } > > @@ -772,6 +782,8 @@ static int virtnet_close(struct net_devi > > { > > struct virtnet_info *vi = netdev_priv(dev); > > > > + /* Make sure refill_work doesn't re-enable napi! */ > > + cancel_delayed_work_sync(&vi->refill); > > napi_disable(&vi->napi); > > > > return 0; > > @@ -1082,7 +1094,6 @@ static int virtnet_probe(struct virtio_d > > > > unregister: > > unregister_netdev(dev); > > - cancel_delayed_work_sync(&vi->refill); > > free_vqs: > > vdev->config->del_vqs(vdev); > > free_stats: > > @@ -1121,9 +1132,7 @@ static void __devexit virtnet_remove(str > > /* Stop all the virtqueues. */ > > vdev->config->reset(vdev); > > > > - > > unregister_netdev(vi->dev); > > - cancel_delayed_work_sync(&vi->refill); > > > > /* Free unused buffers in both send and recv, if any. */ > > free_unused_bufs(vi); -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html