tg3: Fix RSS ring refill race condition

The RSS feature in tg3 hardware has only one rx producer ring for all
RSS rings.  NAPI vector 1 is special and handles the refilling of the
rx producer ring on behalf of all RSS rings.  There is a race condition
between these RSS NAPIs and the NAPI[1].  If NAPI[1] finishes checking
for refill and then another RSS ring empties the rx producer ring
before NAPI[1] exits NAPI, the chip will be completely out of SKBs in
the rx producer ring.

We fix this by adding a flag tp->rx_refill and rely on napi_schedule()/
napi_complete() to help synchronize it to close the race condition.

Update driver version to 3.123.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 3 deletions

diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index b0657466041d..7b71387cf93c 100644
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -89,10 +89,10 @@ static inline void _tg3_flag_clear(enum TG3_FLAGS flag, unsigned long *bits)
 
 #define DRV_MODULE_NAME         "tg3"
 #define TG3_MAJ_NUM                     3
-#define TG3_MIN_NUM                     122
+#define TG3_MIN_NUM                     123
 #define DRV_MODULE_VERSION      \
         __stringify(TG3_MAJ_NUM) "." __stringify(TG3_MIN_NUM)
-#define DRV_MODULE_RELDATE      "December 7, 2011"
+#define DRV_MODULE_RELDATE      "March 21, 2012"
 
 #define RESET_KIND_SHUTDOWN     0
 #define RESET_KIND_INIT         1
@@ -5953,8 +5953,10 @@ next_pkt_nopost:
                 tpr->rx_std_prod_idx = std_prod_idx & tp->rx_std_ring_mask;
                 tpr->rx_jmb_prod_idx = jmb_prod_idx & tp->rx_jmb_ring_mask;
 
-                if (tnapi != &tp->napi[1])
+                if (tnapi != &tp->napi[1]) {
+                        tp->rx_refill = true;
                         napi_schedule(&tp->napi[1].napi);
+                }
         }
 
         return received;
@@ -6134,6 +6136,7 @@ static int tg3_poll_work(struct tg3_napi *tnapi, int work_done, int budget)
                 u32 std_prod_idx = dpr->rx_std_prod_idx;
                 u32 jmb_prod_idx = dpr->rx_jmb_prod_idx;
 
+                tp->rx_refill = false;
                 for (i = 1; i < tp->irq_cnt; i++)
                         err |= tg3_rx_prodring_xfer(tp, dpr,
                                                     &tp->napi[i].prodring);
@@ -6197,9 +6200,25 @@ static int tg3_poll_msix(struct napi_struct *napi, int budget)
                 /* check for RX/TX work to do */
                 if (likely(sblk->idx[0].tx_consumer == tnapi->tx_cons &&
                            *(tnapi->rx_rcb_prod_idx) == tnapi->rx_rcb_ptr)) {
+
+                        /* This test here is not race free, but will reduce
+                         * the number of interrupts by looping again.
+                         */
+                        if (tnapi == &tp->napi[1] && tp->rx_refill)
+                                continue;
+
                         napi_complete(napi);
                         /* Reenable interrupts. */
                         tw32_mailbox(tnapi->int_mbox, tnapi->last_tag << 24);
+
+                        /* This test here is synchronized by napi_schedule()
+                         * and napi_complete() to close the race condition.
+                         */
+                        if (unlikely(tnapi == &tp->napi[1] && tp->rx_refill)) {
+                                tw32(HOSTCC_MODE, tp->coalesce_mode |
+                                                  HOSTCC_MODE_ENABLE |
+                                                  tnapi->coal_now);
+                        }
                         mmiowb();
                         break;
                 }