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>

diff --git a/drivers/net/bnx2x_main.c b/drivers/net/bnx2x_main.c
index 5adf2a0..ed785a3 100644 (file)
--- 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;
 }