From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Simek Subject: Re: Generic DMA - BUG_ON Date: Wed, 20 Jan 2010 12:18:04 +0100 Message-ID: <4B56E66C.50004@monstr.eu> References: <1263982111-24123-1-git-send-email-monstr@monstr.eu> <20100120105350.GA23394@flint.arm.linux.org.uk> <20100120110031.GD8665@amd.com> Reply-To: monstr@monstr.eu Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-fx0-f225.google.com ([209.85.220.225]:54057 "EHLO mail-fx0-f225.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752420Ab0ATLTt (ORCPT ); Wed, 20 Jan 2010 06:19:49 -0500 In-Reply-To: <20100120110031.GD8665@amd.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Joerg Roedel Cc: linux-kernel@vger.kernel.org, michal.simek@petalogix.com, arnd@arndb.de, linux-arch@vger.kernel.org, fujita.tomonori@lab.ntt.co.jp, akpm@linux-foundation.org, mingo@elte.hu Joerg Roedel wrote: > On Wed, Jan 20, 2010 at 10:53:50AM +0000, Russell King wrote: >> and ops is NULL, then this code will oops; you will get a full register >> dump and backtrace. You can use this information along with markup_oops.pl >> to find out where the problem is. > > You can't rely on the oops if the code runs in process context. The > process may have address 0 mapped which would result in a security hole. > We had two of these bugs last year. That's the same problem which I had some days ago and Microblaze misses valuable backtrace (because we don't have FP or constant frame size). > > But I don't see any point in checking for dma_ops != NULL too. Any > developer would mention such a bug long before init is started. I agree that checking adds extra cycles to every dma-api call. I like as wrote Russel to check if ops exists or not. Let's look at code which is there. dma_map_single_attrs - calls ops->map_page without any checking The same for dma_map_sg_attrs, dma_map_page The rest of functions is ok. If any checking will be there, I don't have any problem with it. Michal > > Joerg > > -- Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/ Microblaze U-BOOT custodian