On Monday, February 04, 2013 04:28:28 PM Johannes Berg wrote:
> On Mon, 2013-02-04 at 16:48 +0530, Amit Shakya wrote:
> > @@ -2790,7 +2791,20 @@ static void ieee80211_rx_handlers(struct ieee80211_rx_data *rx)
> >
> > rx->local->running_rx_handler = true;
> >
> > - while ((skb = __skb_dequeue(&rx->local->rx_skb_queue))) {
> > + skb_queue_walk_safe(&rx->local->rx_skb_queue, skb, tmp) {
> > + if (!skb)
> > + break;
> > + hdr = (struct ieee80211_hdr *) skb->data;
> > + /*
> > + * Additional check to ensure that the packets corresponding
> > + * to same sta entry as in rx->sta are de-queued. The queue
> > + * can have different interface packets in case of multiple vifs
> > + */
> > + if ((rx->sta && hdr) && (ieee80211_is_data(hdr->frame_control))
> > + && (memcmp(rx->sta->sta.addr, hdr->addr2, ETH_ALEN)))
> > + continue;
> > + __skb_unlink(skb, &rx->local->rx_skb_queue);
>
> Christian, is there any reason to not just have the queue be on the
> stack, and use a separate spinlock in the local struct to lock out the
> unwanted concurrency?
Let's see.
The original "AMPDU rx reorder timeout timer" had the rx_skb_queue (frames)
on the stack. But that didn't work because the rx-path isn't thread-safe. This
issue was addressed by "mac80211: serialize rx path workers" (24a8fda).
Interestingly, the RFC [1] of this patch mentioned the reason why I/we didn't
go for a rx-path lock:
" 1. Locking is easy to implement but hard to maintain.
Furthermore, Johannes worked very hard to get rid
of as many as possible."
> It seems to me that should work just as well, since there are never frames
> on the rx_skb_queue for very long, right?
Yes it should. At least we didn't find anything wrong with it back then.
Regards,
Christian
[1] <http://article.gmane.org/gmane.linux.kernel.wireless.general/62240>
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