From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH 0/4] revert the commit 22a9189f (cdrom: use kmalloced buffers instead of buffers on stack) Date: Wed, 21 May 2008 18:18:47 -0700 (PDT) Message-ID: <20080521.181847.157652663.davem@davemloft.net> References: <1211259514-9131-1-git-send-email-fujita.tomonori@lab.ntt.co.jp> <20080521221113.GA12695@alpha.franken.de> <20080522095506E.tomof@acm.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:50980 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1762848AbYEVBSw (ORCPT ); Wed, 21 May 2008 21:18:52 -0400 In-Reply-To: <20080522095506E.tomof@acm.org> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: fujita.tomonori@lab.ntt.co.jp Cc: tsbogend@alpha.franken.de, linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, jens.axboe@oracle.com, bzolnier@gmail.com, James.Bottomley@HansenPartnership.com, jeff@garzik.org, akpm@linux-foundation.org From: FUJITA Tomonori Date: Thu, 22 May 2008 10:13:31 +0900 > DMA on stack is forbidden because of non coherent architecutes and > architectures can't uses stack addresses for DMA? What architectures > can't uses stack addresses for DMA? Would it be better to just forbid > using stack addresses for DMA on all the architectures at all times? Rather, the real problem is that some architectures map the kernel stack virtually, and as a result virt_to_page() and things like that will not work. It really is fully not working to put DMA buffers on the stack in these cases.