[TG3]: Eliminate all hw IRQ handler spinlocks.

Move all driver spinlocks to be taken at sw IRQ
context only.

This fixes the skb_copy() we were doing with hw
IRQs disabled (which is illegal and triggers a
BUG() with HIGHMEM enabled).  It also simplifies
the locking all over the driver tremendously.

We accomplish this feat by creating a special
sequence to synchronize with the hw IRQ handler
using a binary state and synchronize_irq().
This idea is from Herbert Xu.

Thanks to Michael Chan for helping to track down
all of the race conditions in initial versions
of this code.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/tg3.h

@@ -2006,17 +2006,31 @@ struct tg3_ethtool_stats {
 struct tg3 {
 	/* begin "general, frequently-used members" cacheline section */
 
+	/* If the IRQ handler (which runs lockless) needs to be
+	 * quiesced, the following bitmask state is used.  The
+	 * SYNC flag is set by non-IRQ context code to initiate
+	 * the quiescence.
+	 *
+	 * When the IRQ handler notices that SYNC is set, it
+	 * disables interrupts and returns.
+	 *
+	 * When all outstanding IRQ handlers have returned after
+	 * the SYNC flag has been set, the setter can be assured
+	 * that interrupts will no longer get run.
+	 *
+	 * In this way all SMP driver locks are never acquired
+	 * in hw IRQ context, only sw IRQ context or lower.
+	 */
+	unsigned int			irq_sync;
+
 	/* SMP locking strategy:
 	 *
 	 * lock: Held during all operations except TX packet
 	 *       processing.
 	 *
-	 * tx_lock: Held during tg3_start_xmit{,_4gbug} and tg3_tx
+	 * tx_lock: Held during tg3_start_xmit and tg3_tx
 	 *
-	 * If you want to shut up all asynchronous processing you must
-	 * acquire both locks, 'lock' taken before 'tx_lock'.  IRQs must
-	 * be disabled to take 'lock' but only softirq disabling is
-	 * necessary for acquisition of 'tx_lock'.
+	 * Both of these locks are to be held with BH safety.
 	 */
 	spinlock_t			lock;
 	spinlock_t			indirect_lock;