netdev - Re: [PATCH net-next v1 13/19] virtio_net: xsk: tx: virtnet_free_old

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Date: Thu, 19 Oct 2023 04:42:56 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next v1 13/19] virtio_net: xsk: tx:
 virtnet_free_old_xmit() distinguishes xsk buffer

On Thu, Oct 19, 2023 at 03:13:48PM +0800, Xuan Zhuo wrote:
> On Thu, 19 Oct 2023 02:38:16 -0400, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> > On Tue, Oct 17, 2023 at 10:02:05AM +0800, Xuan Zhuo wrote:
> > > On Mon, 16 Oct 2023 16:44:34 -0700, Jakub Kicinski <kuba@...nel.org> wrote:
> > > > On Mon, 16 Oct 2023 20:00:27 +0800 Xuan Zhuo wrote:
> > > > > @@ -305,9 +311,15 @@ static inline void virtnet_free_old_xmit(struct virtnet_sq *sq, bool in_napi,
> > > > >
> > > > >  			stats->bytes += xdp_get_frame_len(frame);
> > > > >  			xdp_return_frame(frame);
> > > > > +		} else {
> > > > > +			stats->bytes += virtnet_ptr_to_xsk(ptr);
> > > > > +			++xsknum;
> > > > >  		}
> > > > >  		stats->packets++;
> > > > >  	}
> > > > > +
> > > > > +	if (xsknum)
> > > > > +		xsk_tx_completed(sq->xsk.pool, xsknum);
> > > > >  }
> > > >
> > > > sparse complains:
> > > >
> > > > drivers/net/virtio/virtio_net.h:322:41: warning: incorrect type in argument 1 (different address spaces)
> > > > drivers/net/virtio/virtio_net.h:322:41:    expected struct xsk_buff_pool *pool
> > > > drivers/net/virtio/virtio_net.h:322:41:    got struct xsk_buff_pool
> > > > [noderef] __rcu *pool
> > > >
> > > > please build test with W=1 C=1
> > >
> > > OK. I will add C=1 to may script.
> > >
> > > Thanks.
> >
> > And I hope we all understand, rcu has to be used properly it's not just
> > about casting the warning away.
> 
> 
> Yes. I see. I will use rcu_dereference() and rcu_read_xxx().
> 
> Thanks.

When you do, pls don't forget to add comments documenting what does
rcu_read_lock and synchronize_rcu.


-- 
MST