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sched: qdisc_reset_all_tx is calling qdisc_reset without qdisc_lock

PATCH Applied Jeff Kirsher 2 participants 4 messages Jul 1, 2010 – Jul 3, 2010

Subsystems (2)
Networking Network drivers
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Jeff Kirsher

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#0 lore raw

PATCH 1/2 sched: qdisc_reset_all_tx is calling qdisc_reset without qdisc_lock

From: John Fastabend <[email protected]>

When calling qdisc_reset() the qdisc lock needs to be held. In this case there is at least one driver i4l which is using this without holding the lock. Add the locking here.

Signed-off-by John Fastabend <[email protected]>
Signed-off-by Jeff Kirsher <[email protected]>

---

 include/net/sch_generic.h |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)
include/net/sch_generic.h +10 -2
index 03ca5d8..ba749be 100644
@@ -317,8 +317,16 @@ extern void tcf_destroy_chain(struct tcf_proto **fl);
 static inline void qdisc_reset_all_tx(struct net_device *dev)
 {
 	unsigned int i;
-	for (i = 0; i < dev->num_tx_queues; i++)
-		qdisc_reset(netdev_get_tx_queue(dev, i)->qdisc);
+	struct Qdisc *qdisc;
+
+	for (i = 0; i < dev->num_tx_queues; i++) {
+		qdisc = netdev_get_tx_queue(dev, i)->qdisc;
+		if (qdisc) {
+			spin_lock_bh(qdisc_lock(qdisc));
+			qdisc_reset(qdisc);
+			spin_unlock_bh(qdisc_lock(qdisc));
+		}
+	}
 }
 
 /* Are all TX queues of the device empty?  */
author
#1 lore raw

PATCH 2/2 net: decreasing real_num_tx_queues needs to flush qdisc

From: John Fastabend <[email protected]>

Reducing real_num_queues needs to flush the qdisc otherwise skbs with queue_mappings greater then real_num_tx_queues can be sent to the underlying driver.

The flow for this is,

dev_queue_xmit()

	dev_pick_tx()
		skb_tx_hash()  => hash using real_num_tx_queues
		skb_set_queue_mapping()
	...
	qdisc_enqueue_root() => enqueue skb on txq from hash

...
dev->real_num_tx_queues -= n
...
sch_direct_xmit()
dev_hard_start_xmit()
ndo_start_xmit(skb,dev) => skb queue set with old hash

skbs are enqueued on the qdisc with skb->queue_mapping set 0 < queue_mappings < real_num_tx_queues. When the driver decreases real_num_tx_queues skb's may be dequeued from the qdisc with a queue_mapping greater then real_num_tx_queues.

This fixes a case in ixgbe where this was occurring with DCB and FCoE. Because the driver is using queue_mapping to map skbs to tx descriptor rings we can potentially map skbs to rings that no longer exist.

Signed-off-by John Fastabend <[email protected]>
Tested-by Ross Brattain <[email protected]>
Signed-off-by Jeff Kirsher <[email protected]>

---

 drivers/net/ixgbe/ixgbe_main.c |    2 +-
 include/linux/netdevice.h      |    3 +++
 include/net/sch_generic.h      |   12 ++++++++----
 net/core/dev.c                 |   18 ++++++++++++++++++
 4 files changed, 30 insertions(+), 5 deletions(-)
drivers/net/ixgbe/ixgbe_main.c +1 -1
index a0b3316..7b5d976 100644
@@ -4001,7 +4001,7 @@ static void ixgbe_set_num_queues(struct ixgbe_adapter *adapter)
 
 done:
 	/* Notify the stack of the (possibly) reduced Tx Queue count. */
-	adapter->netdev->real_num_tx_queues = adapter->num_tx_queues;
+	netif_set_real_num_tx_queues(adapter->netdev, adapter->num_tx_queues);
 }
 
 static void ixgbe_acquire_msix_vectors(struct ixgbe_adapter *adapter,
include/linux/netdevice.h +3 -0
index 40291f3..5e6188d 100644
@@ -1656,6 +1656,9 @@ static inline int netif_is_multiqueue(const struct net_device *dev)
 	return (dev->num_tx_queues > 1);
 }
 
+extern void netif_set_real_num_tx_queues(struct net_device *dev,
+					 unsigned int txq);
+
 /* Use this variant when it is known for sure that it
  * is executing from hardware interrupt context or with hardware interrupts
  * disabled.
include/net/sch_generic.h +8 -4
index ba749be..433604b 100644
@@ -313,13 +313,12 @@ extern void qdisc_calculate_pkt_len(struct sk_buff *skb,
 extern void tcf_destroy(struct tcf_proto *tp);
 extern void tcf_destroy_chain(struct tcf_proto **fl);
 
-/* Reset all TX qdiscs of a device.  */
-static inline void qdisc_reset_all_tx(struct net_device *dev)
+/* Reset all TX qdiscs greater then index of a device.  */
+static inline void qdisc_reset_all_tx_gt(struct net_device *dev, unsigned int i)
 {
-	unsigned int i;
 	struct Qdisc *qdisc;
 
-	for (i = 0; i < dev->num_tx_queues; i++) {
+	for (; i < dev->num_tx_queues; i++) {
 		qdisc = netdev_get_tx_queue(dev, i)->qdisc;
 		if (qdisc) {
 			spin_lock_bh(qdisc_lock(qdisc));

@@ -329,6 +328,11 @@ static inline void qdisc_reset_all_tx(struct net_device *dev)
 	}
 }
 
+static inline void qdisc_reset_all_tx(struct net_device *dev)
+{
+	qdisc_reset_all_tx_gt(dev, 0);
+}
+
 /* Are all TX queues of the device empty?  */
 static inline bool qdisc_all_tx_empty(const struct net_device *dev)
 {
net/core/dev.c +18 -0
index 2b3bf53..723a347 100644
@@ -1553,6 +1553,24 @@ static void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
 	rcu_read_unlock();
 }
 
+/*
+ * Routine to help set real_num_tx_queues. To avoid skbs mapped to queues
+ * greater then real_num_tx_queues stale skbs on the qdisc must be flushed.
+ */
+void netif_set_real_num_tx_queues(struct net_device *dev, unsigned int txq)
+{
+	unsigned int real_num = dev->real_num_tx_queues;
+
+	if (unlikely(txq > dev->num_tx_queues))
+		;
+	else if (txq > real_num)
+		dev->real_num_tx_queues = txq;
+	else if (txq < real_num) {
+		dev->real_num_tx_queues = txq;
+		qdisc_reset_all_tx_gt(dev, txq);
+	}
+}
+EXPORT_SYMBOL(netif_set_real_num_tx_queues);
 
 static inline void __netif_reschedule(struct Qdisc *q)
 {
maintainer Applied
#2 lore raw

Re: [net-2.6 PATCH 2/2] net: decreasing real_num_tx_queues needs to flush qdisc

From: Jeff Kirsher <[email protected]>
Date: Thu, 01 Jul 2010 16:21:57 -0700

Quoted 26 lines

From: John Fastabend <[email protected]>

Reducing real_num_queues needs to flush the qdisc otherwise skbs with queue_mappings greater then real_num_tx_queues can be sent to the underlying driver.

The flow for this is,

dev_queue_xmit()

	dev_pick_tx()
		skb_tx_hash()  => hash using real_num_tx_queues
		skb_set_queue_mapping()
	...
	qdisc_enqueue_root() => enqueue skb on txq from hash

...
dev->real_num_tx_queues -= n
...
sch_direct_xmit()
dev_hard_start_xmit()
ndo_start_xmit(skb,dev) => skb queue set with old hash

skbs are enqueued on the qdisc with skb->queue_mapping set 0 < queue_mappings < real_num_tx_queues. When the driver decreases real_num_tx_queues skb's may be dequeued from the qdisc with a queue_mapping greater then real_num_tx_queues.

Quoted 8 lines

This fixes a case in ixgbe where this was occurring with DCB and FCoE. Because the driver is using queue_mapping to map skbs to tx descriptor rings we can potentially map skbs to rings that no longer exist.

Signed-off-by John Fastabend <[email protected]>
Tested-by Ross Brattain <[email protected]>
Signed-off-by Jeff Kirsher <[email protected]>

Applied.

maintainer Applied
#3 lore raw
In reply to Jeff Kirsher

From: Jeff Kirsher <[email protected]>
Date: Thu, 01 Jul 2010 16:21:35 -0700

Quoted 8 lines

From: John Fastabend <[email protected]>

When calling qdisc_reset() the qdisc lock needs to be held. In this case there is at least one driver i4l which is using this without holding the lock. Add the locking here.

Signed-off-by John Fastabend <[email protected]>
Signed-off-by Jeff Kirsher <[email protected]>

Applied.