bnx2x: Tx barriers and locks

[Resending with the proper subject. Sorry for the mess. ]

This patch is based on the RFC of Stanislaw Gruszka.

More specifically it fixes two possible races:
- One, described by Stanislaw, may lead to permanent disabling of the Tx
queue.
This is fixed by adding the smp_wmb() to propagate the BD consumer
change towards the memory.
- Second may lead to bnx2x_start_xmit() returning NETDEV_TX_BUSY.
This is fixed by taking a tx_lock() before rechecking the number of
available Tx BDs.

thanks,
vlad

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Vladislav Zolotarov <vladz@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 9 deletions

diff --git a/drivers/net/bnx2x_main.c b/drivers/net/bnx2x_main.c
index 5adf2a05246f..ed785a30e98b 100644
--- a/drivers/net/bnx2x_main.c
+++ b/drivers/net/bnx2x_main.c
@@ -57,8 +57,8 @@
 #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>
@@ -957,21 +957,34 @@ 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_wmb();
+
         /* TBD need a thresh? */
         if (unlikely(netif_tx_queue_stopped(txq))) {
-
-                /* 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.
+                /* 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
                  */
-                smp_mb();
+
+                __netif_tx_lock(txq, smp_processor_id());
 
                 if ((netif_tx_queue_stopped(txq)) &&
                     (bp->state == BNX2X_STATE_OPEN) &&
                     (bnx2x_tx_avail(fp) >= MAX_SKB_FRAGS + 3))
                         netif_tx_wake_queue(txq);
+
+                __netif_tx_unlock(txq);
         }
         return 0;
 }