-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.
+commit 9a5d2bd99e0dfe9a31b3c160073ac445ba3d773f
+Author: David Woodhouse <dwmw2@infradead.org>
+Date: Sun Apr 8 10:01:44 2012 +0000
-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.
+ 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 <David.Woodhouse@intel.com>
+ Signed-off-by: David S. Miller <davem@davemloft.net>
-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.
+commit e675f0cc9a872fd152edc0c77acfed19bf28b81e
+Author: David Woodhouse <dwmw2@infradead.org>
+Date: Mon Mar 26 00:03:42 2012 +0000
-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.
+ 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 <David.Woodhouse@intel.com>
+ Signed-off-by: David S. Miller <davem@davemloft.net>
-Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
+
+diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
+index 159da29..21d7151 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
-@@ -235,7 +235,7 @@ struct ppp_net {
- /* Prototypes. */
- static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
- struct file *file, unsigned int cmd, unsigned long arg);
--static void ppp_xmit_process(struct ppp *ppp);
-+static int ppp_xmit_process(struct ppp *ppp);
- static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
- static void ppp_push(struct ppp *ppp);
- static void ppp_channel_push(struct channel *pch);
-@@ -968,9 +968,9 @@ ppp_start_xmit(struct sk_buff *skb, stru
+@@ -968,7 +968,6 @@ ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
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);
-+ if (!ppp_xmit_process(ppp))
-+ netif_stop_queue(dev);
+ ppp_xmit_process(ppp);
return NETDEV_TX_OK;
-
- outf:
-@@ -1048,10 +1048,11 @@ static void ppp_setup(struct net_device
- * Called to do any work queued up on the transmit side
- * that can now be done.
- */
--static void
-+static int
- ppp_xmit_process(struct ppp *ppp)
- {
- struct sk_buff *skb;
-+ int ret = 0;
-
- ppp_xmit_lock(ppp);
- if (!ppp->closing) {
-@@ -1061,10 +1062,13 @@ ppp_xmit_process(struct ppp *ppp)
- ppp_send_frame(ppp, skb);
- /* If there's no work left to do, tell the core net
+@@ -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))
-+ if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq)) {
+ if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq))
netif_wake_queue(ppp->dev);
-+ ret = 1;
-+ }
++ else
++ netif_stop_queue(ppp->dev);
}
ppp_xmit_unlock(ppp);
-+ return ret;
}
-
- static inline struct sk_buff *
-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.
+commit 9a5d2bd99e0dfe9a31b3c160073ac445ba3d773f
+Author: David Woodhouse <dwmw2@infradead.org>
+Date: Sun Apr 8 10:01:44 2012 +0000
-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.
+ 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 <David.Woodhouse@intel.com>
+ Signed-off-by: David S. Miller <davem@davemloft.net>
-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.
+commit e675f0cc9a872fd152edc0c77acfed19bf28b81e
+Author: David Woodhouse <dwmw2@infradead.org>
+Date: Mon Mar 26 00:03:42 2012 +0000
-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.
+ 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 <David.Woodhouse@intel.com>
+ Signed-off-by: David S. Miller <davem@davemloft.net>
-Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
+
+diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
+index 159da29..21d7151 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
-@@ -235,7 +235,7 @@ struct ppp_net {
- /* Prototypes. */
- static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
- struct file *file, unsigned int cmd, unsigned long arg);
--static void ppp_xmit_process(struct ppp *ppp);
-+static int ppp_xmit_process(struct ppp *ppp);
- static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
- static void ppp_push(struct ppp *ppp);
- static void ppp_channel_push(struct channel *pch);
-@@ -968,9 +968,9 @@ ppp_start_xmit(struct sk_buff *skb, stru
+@@ -968,7 +968,6 @@ ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
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);
-+ if (!ppp_xmit_process(ppp))
-+ netif_stop_queue(dev);
+ ppp_xmit_process(ppp);
return NETDEV_TX_OK;
-
- outf:
-@@ -1048,10 +1048,11 @@ static void ppp_setup(struct net_device
- * Called to do any work queued up on the transmit side
- * that can now be done.
- */
--static void
-+static int
- ppp_xmit_process(struct ppp *ppp)
- {
- struct sk_buff *skb;
-+ int ret = 0;
-
- ppp_xmit_lock(ppp);
- if (!ppp->closing) {
-@@ -1061,10 +1062,13 @@ ppp_xmit_process(struct ppp *ppp)
- ppp_send_frame(ppp, skb);
- /* If there's no work left to do, tell the core net
+@@ -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))
-+ if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq)) {
+ if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq))
netif_wake_queue(ppp->dev);
-+ ret = 1;
-+ }
++ else
++ netif_stop_queue(ppp->dev);
}
ppp_xmit_unlock(ppp);
-+ return ret;
}
-
- static inline struct sk_buff *
projects / openwrt.git / commitdiff