From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: linux-kernel@vger.kernel.org, Jakub Kicinski <kuba@kernel.org>,
Wei Wang <weiwan@google.com>, David Miller <davem@davemloft.net>,
netdev@vger.kernel.org, Willem de Bruijn <willemb@google.com>,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH RFC v2 3/4] virtio_net: move tx vq operation under tx queue lock
Date: Tue, 13 Apr 2021 10:02:55 -0400 [thread overview]
Message-ID: <20210413100222-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <805053bf-960f-3c34-ce23-012d121ca937@redhat.com>
On Tue, Apr 13, 2021 at 04:54:42PM +0800, Jason Wang wrote:
>
> 在 2021/4/13 下午1:47, Michael S. Tsirkin 写道:
> > It's unsafe to operate a vq from multiple threads.
> > Unfortunately this is exactly what we do when invoking
> > clean tx poll from rx napi.
> > As a fix move everything that deals with the vq to under tx lock.
> >
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > drivers/net/virtio_net.c | 22 +++++++++++++++++++++-
> > 1 file changed, 21 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 16d5abed582c..460ccdbb840e 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1505,6 +1505,8 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
> > struct virtnet_info *vi = sq->vq->vdev->priv;
> > unsigned int index = vq2txq(sq->vq);
> > struct netdev_queue *txq;
> > + int opaque;
> > + bool done;
> > if (unlikely(is_xdp_raw_buffer_queue(vi, index))) {
> > /* We don't need to enable cb for XDP */
> > @@ -1514,10 +1516,28 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
> > txq = netdev_get_tx_queue(vi->dev, index);
> > __netif_tx_lock(txq, raw_smp_processor_id());
> > + virtqueue_disable_cb(sq->vq);
> > free_old_xmit_skbs(sq, true);
> > +
> > + opaque = virtqueue_enable_cb_prepare(sq->vq);
> > +
> > + done = napi_complete_done(napi, 0);
> > +
> > + if (!done)
> > + virtqueue_disable_cb(sq->vq);
> > +
> > __netif_tx_unlock(txq);
> > - virtqueue_napi_complete(napi, sq->vq, 0);
>
>
> So I wonder why not simply move __netif_tx_unlock() after
> virtqueue_napi_complete()?
>
> Thanks
>
Because that calls tx poll which also takes tx lock internally ...
> > + if (done) {
> > + if (unlikely(virtqueue_poll(sq->vq, opaque))) {
> > + if (napi_schedule_prep(napi)) {
> > + __netif_tx_lock(txq, raw_smp_processor_id());
> > + virtqueue_disable_cb(sq->vq);
> > + __netif_tx_unlock(txq);
> > + __napi_schedule(napi);
> > + }
> > + }
> > + }
> > if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
> > netif_tx_wake_queue(txq);
next prev parent reply other threads:[~2021-04-13 14:03 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 5:47 [PATCH RFC v2 0/4] virtio net: spurious interrupt related fixes Michael S. Tsirkin
2021-04-13 5:47 ` [PATCH RFC v2 1/4] virtio: fix up virtio_disable_cb Michael S. Tsirkin
2021-04-13 8:51 ` Jason Wang
2021-04-13 14:01 ` Willem de Bruijn
2021-04-13 19:53 ` Michael S. Tsirkin
2021-04-13 21:44 ` Willem de Bruijn
2021-04-13 22:11 ` Michael S. Tsirkin
2021-04-14 0:24 ` Willem de Bruijn
2021-04-13 5:47 ` [PATCH RFC v2 2/4] virtio_net: disable cb aggressively Michael S. Tsirkin
2021-04-13 8:53 ` Jason Wang
2021-04-13 14:08 ` Willem de Bruijn
2021-04-13 14:33 ` Michael S. Tsirkin
2021-04-13 5:47 ` [PATCH RFC v2 3/4] virtio_net: move tx vq operation under tx queue lock Michael S. Tsirkin
2021-04-13 8:54 ` Jason Wang
2021-04-13 14:02 ` Michael S. Tsirkin [this message]
2021-04-13 14:20 ` Willem de Bruijn
2021-04-13 19:38 ` Michael S. Tsirkin
2021-04-13 5:47 ` [PATCH RFC v2 4/4] virtio_net: move txq wakeups under tx q lock Michael S. Tsirkin
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