commit 9a5d2bd99e0dfe9a31b3c160073ac445ba3d773f Author: David Woodhouse Date: Sun Apr 8 10:01:44 2012 +0000 ppp: Fix race condition with queue start/stop Commit e675f0cc9a872fd152edc0c77acfed19bf28b81e ("ppp: Don't stop and restart queue on every TX packet") introduced a race condition which could leave the net queue stopped even when the channel is no longer busy. By calling netif_stop_queue() from ppp_start_xmit(), based on the return value from ppp_xmit_process() but *after* all the locks have been dropped, we could potentially do so *after* the channel has actually finished transmitting and attempted to re-wake the queue. Fix this by moving the netif_stop_queue() into ppp_xmit_process() under the xmit lock. I hadn't done this previously, because it gets called from other places than ppp_start_xmit(). But I now think it's the better option. The net queue *should* be stopped if the channel becomes congested due to writes from pppd, anyway. Signed-off-by: David Woodhouse Signed-off-by: David S. Miller commit e675f0cc9a872fd152edc0c77acfed19bf28b81e Author: David Woodhouse Date: Mon Mar 26 00:03:42 2012 +0000 ppp: Don't stop and restart queue on every TX packet For every transmitted packet, ppp_start_xmit() will stop the netdev queue and then, if appropriate, restart it. This causes the TX softirq to run, entirely gratuitously. This is "only" a waste of CPU time in the normal case, but it's actively harmful when the PPP device is a TEQL slave — the wakeup will cause the offending device to receive the next TX packet from the TEQL queue, when it *should* have gone to the next slave in the list. We end up seeing large bursts of packets on just *one* slave device, rather than using the full available bandwidth over all slaves. This patch fixes the problem by *not* unconditionally stopping the queue in ppp_start_xmit(). It adds a return value from ppp_xmit_process() which indicates whether the queue should be stopped or not. It *doesn't* remove the call to netif_wake_queue() from ppp_xmit_process(), because other code paths (especially from ppp_output_wakeup()) need it there and it's messy to push it out to the other callers to do it based on the return value. So we leave it in place — it's a no-op in the case where the queue wasn't stopped, so it's harmless in the TX path. Signed-off-by: David Woodhouse Signed-off-by: David S. Miller --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -968,7 +968,6 @@ ppp_start_xmit(struct sk_buff *skb, stru proto = npindex_to_proto[npi]; put_unaligned_be16(proto, pp); - netif_stop_queue(dev); skb_queue_tail(&ppp->file.xq, skb); ppp_xmit_process(ppp); return NETDEV_TX_OK; @@ -1063,6 +1062,8 @@ ppp_xmit_process(struct ppp *ppp) code that we can accept some more. */ if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq)) netif_wake_queue(ppp->dev); + else + netif_stop_queue(ppp->dev); } ppp_xmit_unlock(ppp); }