From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964999AbVIHU2N (ORCPT ); Thu, 8 Sep 2005 16:28:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964997AbVIHU2M (ORCPT ); Thu, 8 Sep 2005 16:28:12 -0400 Received: from zproxy.gmail.com ([64.233.162.205]:25319 "EHLO zproxy.gmail.com") by vger.kernel.org with ESMTP id S964991AbVIHU2K convert rfc822-to-8bit (ORCPT ); Thu, 8 Sep 2005 16:28:10 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:reply-to:to:subject:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=JMHwR4TCmwT4V+5UjtA/I51WfmOAOIqcnWJH8fyaXaTthBqrI76YP2yn5/hifGt2ANWhUJQiJ//IiaXXm+C5tOkXcpuP2wv8CQ4loW0gHuSqDWcI/5nYeK9ttMoFXN/SVPy0DZVP9WnV6jo4VJHPsuibgeA3KuhM/dI8Yy2WlvM= Message-ID: <4789af9e05090813287f05e12a@mail.gmail.com> Date: Thu, 8 Sep 2005 14:28:09 -0600 From: Jim Ramsay Reply-To: jim.ramsay@gmail.com To: Matthew Dharm , linux-usb-users@lists.sourceforge.net, Linux Kernel , linux-scsi@vger.kernel.org Subject: Re: [Linux-usb-users] Possible bug in usb storage (2.6.11 kernel) In-Reply-To: <4789af9e05090812521d9d687b@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Content-Disposition: inline References: <4789af9e05090810142bd3531d@mail.gmail.com> <20050908175852.GA3196@one-eyed-alien.net> <4789af9e05090812521d9d687b@mail.gmail.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 9/8/05, Jim Ramsay wrote: > On 9/8/05, Matthew Dharm wrote: > > On Thu, Sep 08, 2005 at 11:14:36AM -0600, Jim Ramsay wrote: > > > I think I have found a possible bug: > > > [...] > > > I suppose the scsi code could be changed to guarantee that > > > srb->request_buffer is page-aligned or cache-aligned, but that seems > > > like the wrong solution for this bug. > > > > Fixing the SCSI layer is -exactly- the correct solution. The SCSI layer is > > supposed to guarantee us that those buffers are suitable for DMA'ing, and > > apparently it's violating that promise. > > Thanks, I'll check on what buffer I'm actually getting, where it's > allocated, and post back what I find, or how I fixed it. More information: The error only occurrs during device sensing when the srb->request_buffer is assigned as follows, by usb/storage/transport.c in the routine usb_stor_invoke_transport: old_request_buffer = srb->request_buffer; srb->request_buffer = srb->sense_buffer; Now, this is a problem because srb->sense_buffer is defined as follows in the struct scsi_cmnd: #define SCSI_SENSE_BUFFERSIZE 96 unsigned char sense_buffer[SCSI_SENSE_BUFFERSIZE]; Since it is not allocated at runtime there is NO WAY the SCSI layer can possibly guarantee it is page- or cache-aligned and ready for DMA. Any suggestions on best fix for this? Is it still a SCSI-layer issue? Or should USB step up in this case and ensure this buffer is dma-safe itself? -- Jim Ramsay "Me fail English? That's unpossible!"