From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756663AbYDVGdq (ORCPT ); Tue, 22 Apr 2008 02:33:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754580AbYDVGdi (ORCPT ); Tue, 22 Apr 2008 02:33:38 -0400 Received: from brick.kernel.dk ([87.55.233.238]:15227 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754556AbYDVGdh (ORCPT ); Tue, 22 Apr 2008 02:33:37 -0400 Date: Tue, 22 Apr 2008 08:33:33 +0200 From: Jens Axboe To: Thomas Bogendoerfer Cc: Jeff Garzik , Linux Kernel Mailing List , Andrew Morton Subject: Re: cdrom: use kmalloced buffers instead of buffers on stack Message-ID: <20080422063332.GQ12774@kernel.dk> References: <200804220100.m3M10sva024025@hera.kernel.org> <480D46F6.3080305@garzik.org> <20080422054857.GA5940@alpha.franken.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080422054857.GA5940@alpha.franken.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 22 2008, Thomas Bogendoerfer wrote: > On Mon, Apr 21, 2008 at 10:01:26PM -0400, Jeff Garzik wrote: > > > cdrom: use kmalloced buffers instead of buffers on stack > > > > > > If cdrom commands are issued to a scsi drive in most cases the buffer > > > will be > > > filled via dma. This leads to bad stack corruption on non coherent > > > platforms, > > > because the buffers are neither cache line aligned nor is the size a > > > multiple > > > of the cache line size. Using kmalloced buffers avoids this. > > > > > > Signed-off-by: Thomas Bogendoerfer > > > Signed-off-by: Jens Axboe > > >--- > > > drivers/cdrom/cdrom.c | 274 > > > ++++++++++++++++++++++++++++++++----------------- > > > 1 files changed, 181 insertions(+), 93 deletions(-) > > > > Eh... AFAICS this is only really useful in two of the cases converted. > > > > For all the other cases (<= 32 bytes), it is _far_ less complex, far > > less code to simply communicate the additional alignment requirements to > > the compiler. > > > > What about __attribute__ __aligned__? Was that tried? > > I used that while narrowing down the bug. But not only the alignment is > important, but also size needs to be a multiple of the cache line size. > Which means it needs to be 128 bytes for most SGI machines. That > and the following in DMA-mapping.txt > > "This rule also means that you may use neither kernel image addresses > (items in data/text/bss segments), nor module image addresses, nor > stack addresses for DMA." > > let me choose the kmalloc() solution. Which is good, the patch has been due for years :-) -- Jens Axboe