netdev: Fix lockdep warnings in multiqueue configurations.

When support for multiple TX queues were added, the
netif_tx_lock() routines we converted to iterate over
all TX queues and grab each queue's spinlock.

This causes heartburn for lockdep and it's not a healthy
thing to do with lots of TX queues anyways.

So modify this to use a top-level lock and a "frozen"
state for the individual TX queues.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 55 insertions, 31 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index b4d056ceab9..ee583f642a9 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -440,6 +440,7 @@ static inline void napi_synchronize(const struct napi_struct *n)
 enum netdev_queue_state_t
 {
         __QUEUE_STATE_XOFF,
+        __QUEUE_STATE_FROZEN,
 };
 
 struct netdev_queue {
@@ -636,7 +637,7 @@ struct net_device
         unsigned int            real_num_tx_queues;
 
         unsigned long           tx_queue_len;   /* Max frames per queue allowed */
-
+        spinlock_t              tx_global_lock;
 /*
  * One part is mostly used on xmit path (device)
  */
@@ -1099,6 +1100,11 @@ static inline int netif_queue_stopped(const struct net_device *dev)
         return netif_tx_queue_stopped(netdev_get_tx_queue(dev, 0));
 }
 
+static inline int netif_tx_queue_frozen(const struct netdev_queue *dev_queue)
+{
+        return test_bit(__QUEUE_STATE_FROZEN, &dev_queue->state);
+}
+
 /**
  *      netif_running - test if up
  *      @dev: network device
@@ -1475,6 +1481,26 @@ static inline void __netif_tx_lock_bh(struct netdev_queue *txq)
         txq->xmit_lock_owner = smp_processor_id();
 }
 
+static inline int __netif_tx_trylock(struct netdev_queue *txq)
+{
+        int ok = spin_trylock(&txq->_xmit_lock);
+        if (likely(ok))
+                txq->xmit_lock_owner = smp_processor_id();
+        return ok;
+}
+
+static inline void __netif_tx_unlock(struct netdev_queue *txq)
+{
+        txq->xmit_lock_owner = -1;
+        spin_unlock(&txq->_xmit_lock);
+}
+
+static inline void __netif_tx_unlock_bh(struct netdev_queue *txq)
+{
+        txq->xmit_lock_owner = -1;
+        spin_unlock_bh(&txq->_xmit_lock);
+}
+
 /**
  *      netif_tx_lock - grab network device transmit lock
  *      @dev: network device
@@ -1484,12 +1510,23 @@ static inline void __netif_tx_lock_bh(struct netdev_queue *txq)
  */
 static inline void netif_tx_lock(struct net_device *dev)
 {
-        int cpu = smp_processor_id();
         unsigned int i;
+        int cpu;
 
+        spin_lock(&dev->tx_global_lock);
+        cpu = smp_processor_id();
         for (i = 0; i < dev->num_tx_queues; i++) {
                 struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
+
+                /* We are the only thread of execution doing a
+                 * freeze, but we have to grab the _xmit_lock in
+                 * order to synchronize with threads which are in
+                 * the ->hard_start_xmit() handler and already
+                 * checked the frozen bit.
+                 */
                 __netif_tx_lock(txq, cpu);
+                set_bit(__QUEUE_STATE_FROZEN, &txq->state);
+                __netif_tx_unlock(txq);
         }
 }
 
@@ -1499,40 +1536,22 @@ static inline void netif_tx_lock_bh(struct net_device *dev)
         netif_tx_lock(dev);
 }
 
-static inline int __netif_tx_trylock(struct netdev_queue *txq)
-{
-        int ok = spin_trylock(&txq->_xmit_lock);
-        if (likely(ok))
-                txq->xmit_lock_owner = smp_processor_id();
-        return ok;
-}
-
-static inline int netif_tx_trylock(struct net_device *dev)
-{
-        return __netif_tx_trylock(netdev_get_tx_queue(dev, 0));
-}
-
-static inline void __netif_tx_unlock(struct netdev_queue *txq)
-{
-        txq->xmit_lock_owner = -1;
-        spin_unlock(&txq->_xmit_lock);
-}
-
-static inline void __netif_tx_unlock_bh(struct netdev_queue *txq)
-{
-        txq->xmit_lock_owner = -1;
-        spin_unlock_bh(&txq->_xmit_lock);
-}
-
 static inline void netif_tx_unlock(struct net_device *dev)
 {
         unsigned int i;
 
         for (i = 0; i < dev->num_tx_queues; i++) {
                 struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
-                __netif_tx_unlock(txq);
-        }
 
+                /* No need to grab the _xmit_lock here.  If the
+                 * queue is not stopped for another reason, we
+                 * force a schedule.
+                 */
+                clear_bit(__QUEUE_STATE_FROZEN, &txq->state);
+                if (!test_bit(__QUEUE_STATE_XOFF, &txq->state))
+                        __netif_schedule(txq->qdisc);
+        }
+        spin_unlock(&dev->tx_global_lock);
 }
 
 static inline void netif_tx_unlock_bh(struct net_device *dev)
@@ -1556,13 +1575,18 @@ static inline void netif_tx_unlock_bh(struct net_device *dev)
 static inline void netif_tx_disable(struct net_device *dev)
 {
         unsigned int i;
+        int cpu;
 
-        netif_tx_lock_bh(dev);
+        local_bh_disable();
+        cpu = smp_processor_id();
         for (i = 0; i < dev->num_tx_queues; i++) {
                 struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
+
+                __netif_tx_lock(txq, cpu);
                 netif_tx_stop_queue(txq);
+                __netif_tx_unlock(txq);
         }
-        netif_tx_unlock_bh(dev);
+        local_bh_enable();
 }
 
 static inline void netif_addr_lock(struct net_device *dev)