From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753380AbYDVLrv (ORCPT ); Tue, 22 Apr 2008 07:47:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751839AbYDVLrk (ORCPT ); Tue, 22 Apr 2008 07:47:40 -0400 Received: from mo11.iij4u.or.jp ([210.138.174.79]:53106 "EHLO mo11.iij4u.or.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751717AbYDVLrc (ORCPT ); Tue, 22 Apr 2008 07:47:32 -0400 Date: Tue, 22 Apr 2008 20:47:01 +0900 To: tsbogend@alpha.franken.de Cc: jeff@garzik.org, linux-kernel@vger.kernel.org, jens.axboe@oracle.com, akpm@linux-foundation.org Subject: Re: cdrom: use kmalloced buffers instead of buffers on stack From: FUJITA Tomonori In-Reply-To: <20080422054857.GA5940@alpha.franken.de> 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-Transfer-Encoding: 7bit Message-Id: <20080422204637G.tomof@acm.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 22 Apr 2008 07:48:58 +0200 tsbogend@alpha.franken.de (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. Can we advertise such architecture's dma restrictions? For example, if we can update dma_pad_mask and dma_alignment in request_queue, blk_rq_map_kern uses a proper bounce buffer for such architectures. Then we can avoid putting extra complexity in uppper drivers such as cdrom.c