From: Stanislaw Gruszka <sgruszka@redhat.com>
Date: Fri, 30 Apr 2010 08:26:45 -0400
Subject: [net] bnx2x: fix memory barriers
Message-id: <1272616006-3012-1-git-send-email-sgruszka@redhat.com>
Patchwork-id: 24703
O-Subject: [RHEL5.6 PATCH 1/2] bnx2x: fix memory barriers
Bugzilla: 569370
RH-Acked-by: David S. Miller <davem@redhat.com>

From: Stanislaw Gruszka <sgruszka@redhat.com>

BZ#569370

Description:
Fix memory barriers in TX path.

Upstream:
Patches are in Linus tree

commit 9baddeb8c6c7faa7da8706ad629f09ca221850c1
Author: Stanislaw Gruszka <sgruszka@redhat.com>
Date:   Tue Mar 9 06:55:02 2010 +0000

    bnx2x: change smp_mb() comment to conform the true

commit 0efc22f3afa5d8f070a33fea06162d7d9d518e38
Author: Stanislaw Gruszka <sgruszka@redhat.com>
Date:   Tue Mar 9 06:55:01 2010 +0000

    bnx2x: remove not necessary compiler barrier

commit 2d99cf16f42b1979a2c498bb6d09498dbd689978
Author: Stanislaw Gruszka <sgruszka@redhat.com>
Date:   Tue Mar 9 06:55:00 2010 +0000

    bnx2x: use smp_mb() to keep ordering of read write operations

commit c16cc0b464b8876cfd57ce1c1dbcb6f9a6a0bce3
Author: Vladislav Zolotarov <vladz@broadcom.com>
Date:   Sun Feb 28 00:12:02 2010 +0000

    bnx2x: Tx barriers and locks

Testing:
Tested by me by trying to stress driver on 1Gbit link :/

diff --git a/drivers/net/bnx2x_main.c b/drivers/net/bnx2x_main.c
index b68c9d8..2202ad3 100644
--- a/drivers/net/bnx2x_main.c
+++ b/drivers/net/bnx2x_main.c
@@ -56,8 +56,8 @@
 #include "bnx2x_init_ops.h"
 #include "bnx2x_dump.h"
 
-#define DRV_MODULE_VERSION	"1.52.1-6"
-#define DRV_MODULE_RELDATE	"2010/02/16"
+#define DRV_MODULE_VERSION	"1.52.1-7"
+#define DRV_MODULE_RELDATE	"2010/02/28"
 #define BNX2X_BC_VER		0x040200
 
 #include <linux/firmware.h>
@@ -885,7 +885,6 @@ static inline u16 bnx2x_tx_avail(struct bnx2x_fastpath *fp)
 	u16 prod;
 	u16 cons;
 
-	barrier(); /* Tell compiler that prod and cons can change */
 	prod = fp->tx_bd_prod;
 	cons = fp->tx_bd_cons;
 
@@ -950,19 +949,28 @@ static int bnx2x_tx_int(struct bnx2x_fastpath *fp)
 	fp->tx_pkt_cons = sw_cons;
 	fp->tx_bd_cons = bd_cons;
 
+	/* Need to make the tx_bd_cons update visible to start_xmit()
+	 * before checking for netif_tx_queue_stopped().  Without the
+	 * memory barrier, there is a small possibility that
+	 * start_xmit() will miss it and cause the queue to be stopped
+	 * forever.
+	 */
+	smp_mb();
+
 	/* TBD need a thresh? */
 	if (unlikely(netif_queue_stopped(bp->dev))) {
+		/* Taking tx_lock() is needed to prevent reenabling the queue
+		 * while it's empty. This could have happen if rx_action() gets
+		 * suspended in bnx2x_tx_int() after the condition before
+		 * netif_tx_wake_queue(), while tx_action (bnx2x_start_xmit()):
+		 *
+		 * stops the queue->sees fresh tx_bd_cons->releases the queue->
+		 * sends some packets consuming the whole queue again->
+		 * stops the queue
+		 */
 
 		netif_tx_lock(bp->dev);
 
-		/* Need to make the tx_bd_cons update visible to start_xmit()
-		 * before checking for netif_tx_queue_stopped().  Without the
-		 * memory barrier, there is a small possibility that
-		 * start_xmit() will miss it and cause the queue to be stopped
-		 * forever.
-		 */
-		smp_mb();
-
 		if ((netif_queue_stopped(bp->dev)) &&
 		    (bp->state == BNX2X_STATE_OPEN) &&
 		    (bnx2x_tx_avail(fp) >= MAX_SKB_FRAGS + 3))
@@ -11449,9 +11457,12 @@ static int bnx2x_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	if (unlikely(bnx2x_tx_avail(fp) < MAX_SKB_FRAGS + 3)) {
 		netif_stop_queue(dev);
-		/* We want bnx2x_tx_int to "see" the updated tx_bd_prod
-		   if we put Tx into XOFF state. */
+
+		/* paired memory barrier is in bnx2x_tx_int(), we have to keep
+		 * ordering of set_bit() in netif_tx_stop_queue() and read of
+		 * fp->bd_tx_cons */
 		smp_mb();
+
 		fp->eth_q_stats.driver_xoff++;
 		if (bnx2x_tx_avail(fp) >= MAX_SKB_FRAGS + 3)
 			netif_wake_queue(dev);