Re: [PATCH RFC v2 3/4] virtio_net: move tx vq operation under tx queue lock
On Tue, Apr 13, 2021 at 10:20:39AM -0400, Willem de Bruijn wrote:
> On Tue, Apr 13, 2021 at 10:03 AM Michael S. Tsirkin wrote:
> >
> > 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.
>
> Actually, the issue goes back to the napi-tx even without the
> opportunistic cleaning from the receive interrupt, I think? That races
> with processing the vq in start_xmit.
>
> > > > As a fix move everything that deals with the vq to under tx lock.
> > > >
>
> If the above is correct:
>
> Fixes: b92f1e6751a6 ("virtio-net: transmit napi")
>
> > > > Signed-off-by: Michael S. Tsirkin
> > > > ---
> > > > 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;
>
> nit: virtqueue_napi_complete also stores as int opaque, but
> virtqueue_enable_cb_prepare actually returns, and virtqueue_poll
> expects, an unsigned int. In the end, conversion works correctly. But
> cleaner to use the real type.
>
> > > > + 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 ...
>
> which tx poll?
Oh. It's virtqueue_poll actually. I confused it with
virtnet_poll_tx. Right. We can put it back the way it was.
--
MST
Re: [PATCH RFC v2 3/4] virtio_net: move tx vq operation under tx queue lock
On Tue, Apr 13, 2021 at 10:03 AM Michael S. Tsirkin wrote:
>
> 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.
Actually, the issue goes back to the napi-tx even without the
opportunistic cleaning from the receive interrupt, I think? That races
with processing the vq in start_xmit.
> > > As a fix move everything that deals with the vq to under tx lock.
> > >
If the above is correct:
Fixes: b92f1e6751a6 ("virtio-net: transmit napi")
> > > Signed-off-by: Michael S. Tsirkin
> > > ---
> > > 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;
nit: virtqueue_napi_complete also stores as int opaque, but
virtqueue_enable_cb_prepare actually returns, and virtqueue_poll
expects, an unsigned int. In the end, conversion works correctly. But
cleaner to use the real type.
> > > + 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 ...
which tx poll?
Re: [PATCH RFC v2 3/4] virtio_net: move tx vq operation under tx queue lock
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
> > ---
> > 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);
Re: [PATCH RFC v2 3/4] virtio_net: move tx vq operation under tx queue lock
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
---
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
+ 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);
