From mboxrd@z Thu Jan 1 00:00:00 1970 From: Larry Finger Subject: Re: [PATCH V3 for 3.19] rtlwifi: Fix error when accessing unmapped memory in skb Date: Wed, 31 Dec 2014 15:10:50 -0600 Message-ID: <54A4665A.8090906@lwfinger.net> References: <1419996787-17395-1-git-send-email-Larry.Finger@lwfinger.net> <20141231050735.GA20639@zzz> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: kvalo@codeaurora.org, linux-wireless@vger.kernel.org, netdev@vger.kernel.org, Stable To: Eric Biggers Return-path: In-Reply-To: <20141231050735.GA20639@zzz> Sender: stable-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 12/30/2014 11:07 PM, Eric Biggers wrote: > On Tue, Dec 30, 2014 at 09:33:07PM -0600, Larry Finger wrote: >> 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