On Wed, 24 Sep 2008, Breno Leitao wrote:

I just found an issue related to ixgb that seems to be a regression.
After the interface is up and running (packets already transmitted), if
I try to change the MTU, running "ifconfig ethX mtu 70", for example,
causes the following warning[1].

Bisecting I found that the commit that caused this warning is
fc2d14e36c69a8d44a2f5230835b54e95025363e. Reverting it solves the
problem, ie, no more warnings.

Digging further, I found that just removing the following line added
by fc2d14e36c69a8d44a2f5230835b54e95025363e's patch
"buffer_info->dma = 0;", also solves the problem.

Thanks for the report, I think this patch should fix it.  Please test and 
let us know.  This was compile tested only.

----

From: Jesse Brandeburg <redacted>

ixgb: fix bug when freeing resources

It was pointed out by Breno Leitao [off-list ref] that
ixgb would crash on PPC when an IOMMU was in use, if change_mtu was
called.

It appears to be a pretty simple issue in the driver that wasn't discovered
because most systems don't run with an IOMMU.  The driver needs to only unmap
buffers that are mapped (duh).

CC: Breno Leitao <redacted>

Signed-off-by: Jesse Brandeburg <redacted>
---
 drivers/net/ixgb/ixgb_main.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ixgb/ixgb_main.c b/drivers/net/ixgb/ixgb_main.c
index aa75385..be3c7dc 100644
--- a/drivers/net/ixgb/ixgb_main.c
+++ b/drivers/net/ixgb/ixgb_main.c

@@ -977,15 +977,17 @@ ixgb_clean_rx_ring(struct ixgb_adapter *adapter)
 
 	for (i = 0; i < rx_ring->count; i++) {
 		buffer_info = &rx_ring->buffer_info[i];
-		if (buffer_info->skb) {
-
+		if (buffer_info->dma) {
 			pci_unmap_single(pdev,
 					 buffer_info->dma,
 					 buffer_info->length,
 					 PCI_DMA_FROMDEVICE);
+			buffer_info->dma = 0;
+			buffer_info->length = 0;
+		}
 
+		if (buffer_info->skb) {
 			dev_kfree_skb(buffer_info->skb);
-
 			buffer_info->skb = NULL;
 		}
 	}