From 61e800cf949926b3d463ca3cf3025d964872774b Mon Sep 17 00:00:00 2001 From: Matt Carlson Date: Wed, 17 Feb 2010 15:16:54 +0000 Subject: [PATCH] tg3: Enforce DMA mapping / skb assignment ordering Michael Chan noted that there is nothing in the code that would prevent the compiler from delaying the access of the "mapping" member of the newly arrived packet until much later. If this happened after the skb = NULL assignment, it is possible for the driver to pass a bad dma_addr value to pci_unmap_single(). To enforce this ordering, we need a write memory barrier. The pairing read memory barrier already exists in tg3_rx_prodring_xfer() under the comments starting with "Ensure that updates to the...". Signed-off-by: Matt Carlson Signed-off-by: Michael Chan Signed-off-by: David S. Miller --- drivers/net/tg3.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c index 385434ff3960..344490e872b4 100644 --- a/drivers/net/tg3.c +++ b/drivers/net/tg3.c @@ -4659,11 +4659,16 @@ static int tg3_rx(struct tg3_napi *tnapi, int budget) if (skb_size < 0) goto drop_it; - ri->skb = NULL; - pci_unmap_single(tp->pdev, dma_addr, skb_size, PCI_DMA_FROMDEVICE); + /* Ensure that the update to the skb happens + * after the usage of the old DMA mapping. + */ + smp_wmb(); + + ri->skb = NULL; + skb_put(skb, len); } else { struct sk_buff *copy_skb; -- 2.39.5