Re: [PATCH V3 for 3.19] rtlwifi: Fix error when accessing unmapped memory in skb

On 12/30/2014 11:07 PM, Eric Biggers wrote:

On Tue, Dec 30, 2014 at 09:33:07PM -0600, Larry Finger wrote:

quoted

v3 - Unmap skb before trying to allocate a new one so as to not leak mapping.

Looks good to me, although I'm not sure about the handling of DMA mapping errors
(perhaps that's something that drivers typically don't even try to handle?).
Anyway, the skb allocation issue appears to be resolved now.  I am running your
patch with an extra hack to inject some occasional skb allocation failures, and
I haven't noticed any problems except dropped packets.

The last time I saw any DMA mapping errors were for some early BCM43xx cards 
that only had 20 bits of DMA addressing space. These Realtek devices have a full 
32 bits of addressing, thus any physical address in the first 4GB of RAM will be 
OK. I suppose that it might be possible to get a physical address outside this 
range for machines with a lot of RAM, but they are unlikely to have wifi interfaces.

Thanks for the testing. The Realtek engineer told me that they are looking at 
this section, and may do a rewrite. I'm waiting to see what happens there before 
considering alternatives. If the number of packets dropped due to skb allocation 
failures is small, then the current code is likely OK.

Larry