[PATCH] pch_gbe: Adding read memory barriers

 From 3b65802e4c5a8827a84022066f10dec4d61c1f22 Mon Sep 17 00:00:00 2001
From: Erwan Velu <redacted>
Date: Mon, 7 May 2012 14:53:17 +0200
Subject: [PATCH 1/1] pch_gbe: Adding read memory barriers

Under a strong incoming packet stream and/or high cpu usage,
the pch_gbe driver reports "Receive CRC Error" and discards packet.

It occurred on an Intel ATOM E620T while running a 300mbit/sec multicast 
network stream leading to a ~100% cpu usage.

Adding rmb() calls before considering the network card's status solve
this issues.

This patch got validated on the 3.2.16 kernel but also apply to the 3.x 
family.

Getting it into stable would be perfect as it solves reliability issues.


Signed-off-by: Erwan Velu <redacted>
---
  .../net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c   |    8 ++++++++
  1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c 

b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
index 48406ca..7746ca3 100644

--- a/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c
+++ b/drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c

@@ -1222,6 +1222,8 @@ static irqreturn_t pch_gbe_intr(int irq, void *data)
  		}
  	}

+	smp_rmb(); /* prevent any other reads before*/
+
  	/* When request status is Receive interruption */
  	if ((int_st & (PCH_GBE_INT_RX_DMA_CMPLT | PCH_GBE_INT_TX_CMPLT)) ||
  	    (adapter->rx_stop_flag == true)) {

@@ -1390,6 +1392,9 @@ pch_gbe_clean_tx(struct pch_gbe_adapter *adapter,

  	i = tx_ring->next_to_clean;
  	tx_desc = PCH_GBE_TX_DESC(*tx_ring, i);
+
+	rmb();  /* prevent any other reads before*/
+
  	pr_debug("gbec_status:0x%04x  dma_status:0x%04x\n",
  		 tx_desc->gbec_status, tx_desc->dma_status);

@@ -1490,6 +1495,9 @@ pch_gbe_clean_rx(struct pch_gbe_adapter *adapter,
  	while (*work_done < work_to_do) {
  		/* Check Rx descriptor status */
  		rx_desc = PCH_GBE_RX_DESC(*rx_ring, i);
+
+		rmb(); /* prevent any other reads before*/
+
  		if (rx_desc->gbec_status == DSC_INIT16)
  			break;
  		cleaned = true;

-- 
1.7.4.4

Your patch doesn't apply to the net-next tree which is what you should
be basing all of your networking patches on:

[davem@bql net-next]$ git am --signoff pch_gbe-Adding-read-memory-barriers.patch 
Applying: pch_gbe: Adding read memory barriers
error: patch failed: drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c:1222
error: drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c: patch does not apply
Patch failed at 0001 pch_gbe: Adding read memory barriers
When you have resolved this problem run "git am --resolved".
If you would prefer to skip this patch, instead run "git am --skip".
To restore the original branch and stop patching run "git am --abort".

Stop rushing things and take your time learning the process.

Otherwise you're going to make more work for maintainers and they
end up grumpy as a result, which you don't want.