Messages in this thread | | | Date | Thu, 8 Sep 2005 14:28:09 -0600 | From | Jim Ramsay <> | Subject | Re: [Linux-usb-users] Possible bug in usb storage (2.6.11 kernel) |
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On 9/8/05, Jim Ramsay <jim.ramsay@gmail.com> wrote: > On 9/8/05, Matthew Dharm <mdharm-kernel@one-eyed-alien.net> 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!" - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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