net: ep93xx_eth: Do not crash unloading module

When we unload the ep93xx_eth, whether we have opened the network
interface or not, we will either hit a kernel paging request error, or a
simple NULL pointer de-reference because:

- if ep93xx_open has been called, we have created a valid DMA mapping
  for ep->descs, when we call ep93xx_stop, we also call
  ep93xx_free_buffers, ep->descs now has a stale value

- if ep93xx_open has not been called, we have a NULL pointer for
  ep->descs, so performing any operation against that address just won't
  work

Fix this by adding a NULL pointer check for ep->descs which means that
ep93xx_free_buffers() was able to successfully tear down the descriptors
and free the DMA cookie as well.

Fixes: 1d22e05df818 ("[PATCH] Cirrus Logic ep93xx ethernet driver")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/cirrus/ep93xx_eth.c b/drivers/net/ethernet/cirrus/ep93xx_eth.c
index de9f7c97d916d3d8d760282e726cf49f4181a56b..9a161e98152978fcfbafa51a959e214426a90bd9 100644 (file)
--- a/drivers/net/ethernet/cirrus/ep93xx_eth.c
+++ b/drivers/net/ethernet/cirrus/ep93xx_eth.c
@@ -468,6 +468,9 @@ static void ep93xx_free_buffers(struct ep93xx_priv *ep)
        struct device *dev = ep->dev->dev.parent;
        int i;
 
+       if (!ep->descs)
+               return;
+
        for (i = 0; i < RX_QUEUE_ENTRIES; i++) {
                dma_addr_t d;
 
@@ -490,6 +493,7 @@ static void ep93xx_free_buffers(struct ep93xx_priv *ep)
 
        dma_free_coherent(dev, sizeof(struct ep93xx_descs), ep->descs,
                                                        ep->descs_dma_addr);
+       ep->descs = NULL;
 }
 
 static int ep93xx_alloc_buffers(struct ep93xx_priv *ep)