On Thursday 01 May 2008 04:02:48 Johannes Berg wrote: > Hi, > > Whenever you run a monitor interface in mac80211, you can see lots of > truesize bugs: > > SKB BUG: Invalid truesize (464) len=307, sizeof(sk_buff)=176 > > It appears to be caused by mac80211's re-injection of the transmitted > frame. For those not familiar, here's what happens: > > When a frame comes in on say wlan0's hard_start_xmit(), it is prepared > for transmission by the code there (802.11 headers added etc.) and then > scheduled to the master interface. Once it arrives on the master > (wmaster0) interface's hard_start_xmit(), it is modified again and > finally handed to the driver. > > When the driver has transmitted the frame (successfully or not) it > reports the status of the transmission to mac80211 including the skb the > driver was given. At that point, things go different depending on > circumstances. > > If no monitor interfaces are present, mac80211 simply orphans the skb > and destroys it. If there are monitor interfaces, it pushes some data > into the skb (the radiotap transmit status) and hands clones of the skb > to netif_rx() for each monitor interface, or the skb itself for the last > interface in the list. Hm, unrelated to this... But I am wondering what happens if the driver adds a device header to the skb. Is that header then also passed up netif_rx()? This doesn't happen for b43, as we use the DMA fragmentation to transmit the header, but it might happen for zd1211rw and others. > All this is in net/mac80211/main.c:ieee80211_tx_status. > > Now, the thing is that the skb truesize bug ONLY occurs when the last > part here is done when a radiotap monitor interface is present, if you > add > > dev_kfree_skb(skb); > return; > > in that function somewhere before the skb_orphan() call it never > happens. Hence, I'm confused. Since I only have a single monitor > interface when this happens, it can't be due to af_packet either, > afaict. > > Can anyone help me diagnose this? Seems the skb->destructor messes it up. -- Greetings Michael. -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
