sfc: Insert read memory barrier after checking MAC statistics flag

This prevents speculative reading of the statistics before the
completion flag.

From: Neil Turton <nturton@solarflare.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

diff --git a/drivers/net/sfc/falcon.c b/drivers/net/sfc/falcon.c
index 70c681e..3a5289f 100644 (file)
--- a/drivers/net/sfc/falcon.c
+++ b/drivers/net/sfc/falcon.c
@@ -1953,8 +1953,10 @@ int falcon_dma_stats(struct efx_nic *efx, unsigned int done_offset)
 
        /* Wait for transfer to complete */
        for (i = 0; i < 400; i++) {
-               if (*(volatile u32 *)dma_done == FALCON_STATS_DONE)
+               if (*(volatile u32 *)dma_done == FALCON_STATS_DONE) {
+                       rmb(); /* Ensure the stats are valid. */
                        return 0;
+               }
                udelay(10);
        }