From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jim Ramsay Subject: Re: [Linux-usb-users] Possible bug in usb storage (2.6.11 kernel) Date: Thu, 8 Sep 2005 14:28:09 -0600 Message-ID: <4789af9e05090813287f05e12a@mail.gmail.com> References: <4789af9e05090810142bd3531d@mail.gmail.com> <20050908175852.GA3196@one-eyed-alien.net> <4789af9e05090812521d9d687b@mail.gmail.com> Reply-To: jim.ramsay@gmail.com Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Return-path: In-Reply-To: <4789af9e05090812521d9d687b@mail.gmail.com> Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org To: Matthew Dharm , linux-usb-users@lists.sourceforge.net, Linux Kernel , linux-scsi@vger.kernel.org List-Id: linux-scsi@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!"