On Tue, 2013-08-13 at 20:32 +0800, hayeswang wrote:
> Oliver Neukum [mailto:oneu...@suse.de]
> > Sent: Tuesday, August 13, 2013 4:49 PM
> > To: Hayeswang
> > Cc: net...@vger.kernel.org; linux-kernel@vger.kernel.org;
> > linux-...@vger.kernel.org
> > Subject: Re: [PATCH net-next 1/3] net/usb/r8152: support aggregation
> >
> [...]
> > > + len_used = 0;
> > > + rx_desc = agg->head;
> > > + rx_data = agg->head;
> > > + smp_wmb();
> > > + pkt_len = le32_to_cpu(rx_desc->opts1) & RX_LEN_MASK;
> > > + len_used += sizeof(struct rx_desc) + pkt_len;
> > > +
> > > + while (urb->actual_length >= len_used) {
> > > + if (pkt_len < ETH_ZLEN)
> > > + break;
> > > +
> > > + pkt_len -= 4; /* CRC */
> > > + rx_data += sizeof(struct rx_desc);
> > > +
> > > + skb = netdev_alloc_skb_ip_align(netdev,
> > > pkt_len);
> > > + if (!skb) {
> > > + stats->rx_dropped++;
> > > + break;
> > > + }
> > > + memcpy(skb->data, rx_data, pkt_len);
> > > + skb_put(skb, pkt_len);
> > > + skb->protocol = eth_type_trans(skb, netdev);
> > > + netif_rx(skb);
> > > + stats->rx_packets++;
> > > + stats->rx_bytes += pkt_len;
> > > +
> > > + rx_data = rx_agg_align(rx_data +
> > pkt_len + 4);
> > > + rx_desc = (struct rx_desc *)rx_data;
> > > + smp_wmb();
> >
> > Against what is the memory barrier?
>
> Excuse me. I don't understand your question. Do you mean the function should
> not
> be used here?
I don't understand what problem the function is supposed to fix. As long
as I don't understand it I cannot say for sure whether it is correct.
There seems no obvious reason for a memory barrier, but there may be a
hidden reason I don't see.
Regards
Oliver
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