net: remove NETDEV_TX_LOCKED support

No more users in the tree, remove NETDEV_TX_LOCKED support.
Adds another hole in softnet_stats struct, but better than keeping
the unused collision counter around.

Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/netdev-features.txt

···
 
  * LLTX driver (deprecated for hardware drivers)
 
-NETIF_F_LLTX should be set in drivers that implement their own locking in
-transmit path or don't need locking at all (e.g. software tunnels).
-In ndo_start_xmit, it is recommended to use a try_lock and return
-NETDEV_TX_LOCKED when the spin lock fails.  The locking should also properly
-protect against other callbacks (the rules you need to find out).
+NETIF_F_LLTX is meant to be used by drivers that don't need locking at all,
+e.g. software tunnels.
 
-Don't use it for new drivers.
+This is also used in a few legacy drivers that implement their
+own locking, don't use it for new (hardware) drivers.
 
  * netns-local device
 

Documentation/networking/netdevices.txt

···
 
 	When the driver sets NETIF_F_LLTX in dev->features this will be
 	called without holding netif_tx_lock. In this case the driver
-	has to lock by itself when needed. It is recommended to use a try lock
-	for this and return NETDEV_TX_LOCKED when the spin lock fails.
-	The locking there should also properly protect against 
-	set_rx_mode. Note that the use of NETIF_F_LLTX is deprecated.
+	has to lock by itself when needed.
+	The locking there should also properly protect against
+	set_rx_mode. WARNING: use of NETIF_F_LLTX is deprecated.
 	Don't use it for new drivers.
 
 	Context: Process with BHs disabled or BH (timer),
···
 	o NETDEV_TX_BUSY Cannot transmit packet, try later 
 	  Usually a bug, means queue start/stop flow control is broken in
 	  the driver. Note: the driver must NOT put the skb in its DMA ring.
-	o NETDEV_TX_LOCKED Locking failed, please retry quickly.
-	  Only valid when NETIF_F_LLTX is set.
 
 ndo_tx_timeout:
 	Synchronization: netif_tx_lock spinlock; all TX queues frozen.

include/linux/netdevice.h

···
 	__NETDEV_TX_MIN	 = INT_MIN,	/* make sure enum is signed */
 	NETDEV_TX_OK	 = 0x00,	/* driver took care of packet */
 	NETDEV_TX_BUSY	 = 0x10,	/* driver tx path was busy*/
-	NETDEV_TX_LOCKED = 0x20,	/* driver tx lock was already taken */
 };
 typedef enum netdev_tx netdev_tx_t;
 
···
  *	the queue before that can happen; it's for obsolete devices and weird
  *	corner cases, but the stack really does a non-trivial amount
  *	of useless work if you return NETDEV_TX_BUSY.
- *        (can also return NETDEV_TX_LOCKED iff NETIF_F_LLTX)
  *	Required; cannot be NULL.
  *
  * netdev_features_t (*ndo_fix_features)(struct net_device *dev,
···
 	/* stats */
 	unsigned int		processed;
 	unsigned int		time_squeeze;
-	unsigned int		cpu_collision;
 	unsigned int		received_rps;
 #ifdef CONFIG_RPS
 	struct softnet_data	*rps_ipi_list;

net/core/net-procfs.c

···
 		   "%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x\n",
 		   sd->processed, sd->dropped, sd->time_squeeze, 0,
 		   0, 0, 0, 0, /* was fastroute */
-		   sd->cpu_collision, sd->received_rps, flow_limit_count);
+		   0,	/* was cpu_collision */
+		   sd->received_rps, flow_limit_count);
 	return 0;
 }
 

net/core/pktgen.c

···
 				     pkt_dev->odevname, ret);
 		pkt_dev->errors++;
 		/* fallthru */
-	case NETDEV_TX_LOCKED:
 	case NETDEV_TX_BUSY:
 		/* Retry it next time */
 		atomic_dec(&(pkt_dev->skb->users));

net/sched/sch_generic.c

···
 	return skb;
 }
 
-static inline int handle_dev_cpu_collision(struct sk_buff *skb,
-					   struct netdev_queue *dev_queue,
-					   struct Qdisc *q)
-{
-	int ret;
-
-	if (unlikely(dev_queue->xmit_lock_owner == smp_processor_id())) {
-		/*
-		 * Same CPU holding the lock. It may be a transient
-		 * configuration error, when hard_start_xmit() recurses. We
-		 * detect it by checking xmit owner and drop the packet when
-		 * deadloop is detected. Return OK to try the next skb.
-		 */
-		kfree_skb_list(skb);
-		net_warn_ratelimited("Dead loop on netdevice %s, fix it urgently!\n",
-				     dev_queue->dev->name);
-		ret = qdisc_qlen(q);
-	} else {
-		/*
-		 * Another cpu is holding lock, requeue & delay xmits for
-		 * some time.
-		 */
-		__this_cpu_inc(softnet_data.cpu_collision);
-		ret = dev_requeue_skb(skb, q);
-	}
-
-	return ret;
-}
-
 /*
  * Transmit possibly several skbs, and handle the return status as
  * required. Holding the __QDISC___STATE_RUNNING bit guarantees that
···
 	if (dev_xmit_complete(ret)) {
 		/* Driver sent out skb successfully or skb was consumed */
 		ret = qdisc_qlen(q);
-	} else if (ret == NETDEV_TX_LOCKED) {
-		/* Driver try lock failed */
-		ret = handle_dev_cpu_collision(skb, txq, q);
 	} else {
 		/* Driver returned NETDEV_TX_BUSY - requeue skb */
 		if (unlikely(ret != NETDEV_TX_BUSY))