From: Ben Hutchings <bhutchings@solarflare.com>
Date: Mon, 1 Sep 2008 11:50:08 +0000 (+0100)
Subject: sfc: Insert read memory barrier after checking MAC statistics flag
X-Git-Tag: v2.6.28-rc1~717^2~195^2~47
X-Git-Url: http://www.pilppa.org/gitweb/gitweb.cgi?a=commitdiff_plain;h=1d0680fd6235e0aa5baf14a8f1ff85eff9dc1fb3;p=linux-2.6-omap-h63xx.git

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 70c681ecdab..3a5289fe8d1 100644
--- 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);
 	}