gianfar: Revive SKB recycling

Before calling gfar_clean_tx_ring() the driver grabs an irqsave
spinlock, and then tries to recycle skbs. But since
skb_recycle_check() returns 0 with IRQs disabled, we'll never
recycle any skbs.

It appears that gfar_clean_tx_ring() and gfar_start_xmit() are
mostly idependent and can work in parallel, except when they
modify num_txbdfree.

So we can drop the lock from most sections and thus fix the skb
recycling.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 19 insertions, 12 deletions

diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
index fde430a0b84b..16def131c390 100644
--- a/drivers/net/gianfar.c
+++ b/drivers/net/gianfar.c
@@ -1928,14 +1928,11 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
         /* total number of fragments in the SKB */
         nr_frags = skb_shinfo(skb)->nr_frags;
 
-        spin_lock_irqsave(&tx_queue->txlock, flags);
-
         /* check if there is space to queue this packet */
         if ((nr_frags+1) > tx_queue->num_txbdfree) {
                 /* no space, stop the queue */
                 netif_tx_stop_queue(txq);
                 dev->stats.tx_fifo_errors++;
-                spin_unlock_irqrestore(&tx_queue->txlock, flags);
                 return NETDEV_TX_BUSY;
         }
 
@@ -1999,6 +1996,20 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
         lstatus |= BD_LFLAG(TXBD_CRC | TXBD_READY) | skb_headlen(skb);
 
         /*
+         * We can work in parallel with gfar_clean_tx_ring(), except
+         * when modifying num_txbdfree. Note that we didn't grab the lock
+         * when we were reading the num_txbdfree and checking for available
+         * space, that's because outside of this function it can only grow,
+         * and once we've got needed space, it cannot suddenly disappear.
+         *
+         * The lock also protects us from gfar_error(), which can modify
+         * regs->tstat and thus retrigger the transfers, which is why we
+         * also must grab the lock before setting ready bit for the first
+         * to be transmitted BD.
+         */
+        spin_lock_irqsave(&tx_queue->txlock, flags);
+
+        /*
          * The powerpc-specific eieio() is used, as wmb() has too strong
          * semantics (it requires synchronization between cacheable and
          * uncacheable mappings, which eieio doesn't provide and which we
@@ -2225,6 +2236,8 @@ static int gfar_clean_tx_ring(struct gfar_priv_tx_q *tx_queue)
         skb_dirtytx = tx_queue->skb_dirtytx;
 
         while ((skb = tx_queue->tx_skbuff[skb_dirtytx])) {
+                unsigned long flags;
+
                 frags = skb_shinfo(skb)->nr_frags;
                 lbdp = skip_txbd(bdp, frags, base, tx_ring_size);
 
@@ -2269,7 +2282,9 @@ static int gfar_clean_tx_ring(struct gfar_priv_tx_q *tx_queue)
                         TX_RING_MOD_MASK(tx_ring_size);
 
                 howmany++;
+                spin_lock_irqsave(&tx_queue->txlock, flags);
                 tx_queue->num_txbdfree += frags + 1;
+                spin_unlock_irqrestore(&tx_queue->txlock, flags);
         }
 
         /* If we freed a buffer, we can restart transmission, if necessary */
@@ -2548,7 +2563,6 @@ static int gfar_poll(struct napi_struct *napi, int budget)
         int tx_cleaned = 0, i, left_over_budget = budget;
         unsigned long serviced_queues = 0;
         int num_queues = 0;
-        unsigned long flags;
 
         num_queues = gfargrp->num_rx_queues;
         budget_per_queue = budget/num_queues;
@@ -2568,14 +2582,7 @@ static int gfar_poll(struct napi_struct *napi, int budget)
                         rx_queue = priv->rx_queue[i];
                         tx_queue = priv->tx_queue[rx_queue->qindex];
 
-                        /* If we fail to get the lock,
-                         * don't bother with the TX BDs */
-                        if (spin_trylock_irqsave(&tx_queue->txlock, flags)) {
-                                tx_cleaned += gfar_clean_tx_ring(tx_queue);
-                                spin_unlock_irqrestore(&tx_queue->txlock,
-                                                        flags);
-                        }
-
+                        tx_cleaned += gfar_clean_tx_ring(tx_queue);
                         rx_cleaned_per_queue = gfar_clean_rx_ring(rx_queue,
                                                         budget_per_queue);
                         rx_cleaned += rx_cleaned_per_queue;