From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756558AbYDVGFE (ORCPT ); Tue, 22 Apr 2008 02:05:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753381AbYDVGEx (ORCPT ); Tue, 22 Apr 2008 02:04:53 -0400 Received: from elvis.franken.de ([193.175.24.41]:58987 "EHLO elvis.franken.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753340AbYDVGEx (ORCPT ); Tue, 22 Apr 2008 02:04:53 -0400 Date: Tue, 22 Apr 2008 07:48:58 +0200 To: Jeff Garzik Cc: Linux Kernel Mailing List , Jens Axboe , Andrew Morton Subject: Re: cdrom: use kmalloced buffers instead of buffers on stack Message-ID: <20080422054857.GA5940@alpha.franken.de> References: <200804220100.m3M10sva024025@hera.kernel.org> <480D46F6.3080305@garzik.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <480D46F6.3080305@garzik.org> User-Agent: Mutt/1.5.13 (2006-08-11) From: tsbogend@alpha.franken.de (Thomas Bogendoerfer) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessary a good idea. [ RFC1925, 2.3 ]