[NET]: Add netif_tx_lock

Various drivers use xmit_lock internally to synchronise with their
transmission routines.  They do so without setting xmit_lock_owner.
This is fine as long as netpoll is not in use.

With netpoll it is possible for deadlocks to occur if xmit_lock_owner
isn't set.  This is because if a printk occurs while xmit_lock is held
and xmit_lock_owner is not set can cause netpoll to attempt to take
xmit_lock recursively.

While it is possible to resolve this by getting netpoll to use
trylock, it is suboptimal because netpoll's sole objective is to
maximise the chance of getting the printk out on the wire.  So
delaying or dropping the message is to be avoided as much as possible.

So the only alternative is to always set xmit_lock_owner.  The
following patch does this by introducing the netif_tx_lock family of
functions that take care of setting/unsetting xmit_lock_owner.

I renamed xmit_lock to _xmit_lock to indicate that it should not be
used directly.  I didn't provide irq versions of the netif_tx_lock
functions since xmit_lock is meant to be a BH-disabling lock.

This is pretty much a straight text substitution except for a small
bug fix in winbond.  It currently uses
netif_stop_queue/spin_unlock_wait to stop transmission.  This is
unsafe as an IRQ can potentially wake up the queue.  So it is safer to
use netif_tx_disable.

The hamradio bits used spin_lock_irq but it is unnecessary as
xmit_lock must never be taken in an IRQ handler.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 16 deletions

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 138ea92ed268..b1e4c5e20ac7 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -72,9 +72,9 @@ void qdisc_unlock_tree(struct net_device *dev)
    dev->queue_lock serializes queue accesses for this device
    AND dev->qdisc pointer itself.
 
-   dev->xmit_lock serializes accesses to device driver.
+   netif_tx_lock serializes accesses to device driver.
 
-   dev->queue_lock and dev->xmit_lock are mutually exclusive,
+   dev->queue_lock and netif_tx_lock are mutually exclusive,
    if one is grabbed, another must be free.
  */
 
@@ -108,7 +108,7 @@ int qdisc_restart(struct net_device *dev)
                  * will be requeued.
                  */
                 if (!nolock) {
-                        if (!spin_trylock(&dev->xmit_lock)) {
+                        if (!netif_tx_trylock(dev)) {
                         collision:
                                 /* So, someone grabbed the driver. */
                                 
@@ -126,8 +126,6 @@ int qdisc_restart(struct net_device *dev)
                                 __get_cpu_var(netdev_rx_stat).cpu_collision++;
                                 goto requeue;
                         }
-                        /* Remember that the driver is grabbed by us. */
-                        dev->xmit_lock_owner = smp_processor_id();
                 }
                 
                 {
@@ -142,8 +140,7 @@ int qdisc_restart(struct net_device *dev)
                                 ret = dev->hard_start_xmit(skb, dev);
                                 if (ret == NETDEV_TX_OK) { 
                                         if (!nolock) {
-                                                dev->xmit_lock_owner = -1;
-                                                spin_unlock(&dev->xmit_lock);
+                                                netif_tx_unlock(dev);
                                         }
                                         spin_lock(&dev->queue_lock);
                                         return -1;
@@ -157,8 +154,7 @@ int qdisc_restart(struct net_device *dev)
                         /* NETDEV_TX_BUSY - we need to requeue */
                         /* Release the driver */
                         if (!nolock) { 
-                                dev->xmit_lock_owner = -1;
-                                spin_unlock(&dev->xmit_lock);
+                                netif_tx_unlock(dev);
                         } 
                         spin_lock(&dev->queue_lock);
                         q = dev->qdisc;
@@ -187,7 +183,7 @@ static void dev_watchdog(unsigned long arg)
 {
         struct net_device *dev = (struct net_device *)arg;
 
-        spin_lock(&dev->xmit_lock);
+        netif_tx_lock(dev);
         if (dev->qdisc != &noop_qdisc) {
                 if (netif_device_present(dev) &&
                     netif_running(dev) &&
@@ -203,7 +199,7 @@ static void dev_watchdog(unsigned long arg)
                                 dev_hold(dev);
                 }
         }
-        spin_unlock(&dev->xmit_lock);
+        netif_tx_unlock(dev);
 
         dev_put(dev);
 }
@@ -227,17 +223,17 @@ void __netdev_watchdog_up(struct net_device *dev)
 
 static void dev_watchdog_up(struct net_device *dev)
 {
-        spin_lock_bh(&dev->xmit_lock);
+        netif_tx_lock_bh(dev);
         __netdev_watchdog_up(dev);
-        spin_unlock_bh(&dev->xmit_lock);
+        netif_tx_unlock_bh(dev);
 }
 
 static void dev_watchdog_down(struct net_device *dev)
 {
-        spin_lock_bh(&dev->xmit_lock);
+        netif_tx_lock_bh(dev);
         if (del_timer(&dev->watchdog_timer))
                 dev_put(dev);
-        spin_unlock_bh(&dev->xmit_lock);
+        netif_tx_unlock_bh(dev);
 }
 
 void netif_carrier_on(struct net_device *dev)
@@ -582,7 +578,7 @@ void dev_deactivate(struct net_device *dev)
         while (test_bit(__LINK_STATE_SCHED, &dev->state))
                 yield();
 
-        spin_unlock_wait(&dev->xmit_lock);
+        spin_unlock_wait(&dev->_xmit_lock);
 }
 
 void dev_init_scheduler(struct net_device *dev)