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78 lines
3.3 KiB
Diff
78 lines
3.3 KiB
Diff
commit 9a5d2bd99e0dfe9a31b3c160073ac445ba3d773f
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Author: David Woodhouse <dwmw2@infradead.org>
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Date: Sun Apr 8 10:01:44 2012 +0000
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ppp: Fix race condition with queue start/stop
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Commit e675f0cc9a872fd152edc0c77acfed19bf28b81e ("ppp: Don't stop and
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restart queue on every TX packet") introduced a race condition which
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could leave the net queue stopped even when the channel is no longer
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busy. By calling netif_stop_queue() from ppp_start_xmit(), based on the
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return value from ppp_xmit_process() but *after* all the locks have been
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dropped, we could potentially do so *after* the channel has actually
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finished transmitting and attempted to re-wake the queue.
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Fix this by moving the netif_stop_queue() into ppp_xmit_process() under
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the xmit lock. I hadn't done this previously, because it gets called
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from other places than ppp_start_xmit(). But I now think it's the better
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option. The net queue *should* be stopped if the channel becomes
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congested due to writes from pppd, anyway.
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Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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commit e675f0cc9a872fd152edc0c77acfed19bf28b81e
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Author: David Woodhouse <dwmw2@infradead.org>
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Date: Mon Mar 26 00:03:42 2012 +0000
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ppp: Don't stop and restart queue on every TX packet
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For every transmitted packet, ppp_start_xmit() will stop the netdev
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queue and then, if appropriate, restart it. This causes the TX softirq
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to run, entirely gratuitously.
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This is "only" a waste of CPU time in the normal case, but it's actively
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harmful when the PPP device is a TEQL slave — the wakeup will cause the
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offending device to receive the next TX packet from the TEQL queue, when
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it *should* have gone to the next slave in the list. We end up seeing
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large bursts of packets on just *one* slave device, rather than using
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the full available bandwidth over all slaves.
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This patch fixes the problem by *not* unconditionally stopping the queue
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in ppp_start_xmit(). It adds a return value from ppp_xmit_process()
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which indicates whether the queue should be stopped or not.
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It *doesn't* remove the call to netif_wake_queue() from
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ppp_xmit_process(), because other code paths (especially from
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ppp_output_wakeup()) need it there and it's messy to push it out to the
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other callers to do it based on the return value. So we leave it in
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place — it's a no-op in the case where the queue wasn't stopped, so it's
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harmless in the TX path.
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Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
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index 159da29..21d7151 100644
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--- a/drivers/net/ppp/ppp_generic.c
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+++ b/drivers/net/ppp/ppp_generic.c
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@@ -968,7 +968,6 @@ ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
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proto = npindex_to_proto[npi];
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put_unaligned_be16(proto, pp);
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- netif_stop_queue(dev);
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skb_queue_tail(&ppp->file.xq, skb);
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ppp_xmit_process(ppp);
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return NETDEV_TX_OK;
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@@ -1063,6 +1062,8 @@ ppp_xmit_process(struct ppp *ppp)
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code that we can accept some more. */
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if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq))
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netif_wake_queue(ppp->dev);
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+ else
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+ netif_stop_queue(ppp->dev);
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}
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ppp_xmit_unlock(ppp);
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}
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