On Thu, Jun 04 2009, FUJITA Tomonori wrote: > On Thu, 04 Jun 2009 10:15:14 +0300 > Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote: > > > On 06/04/2009 09:33 AM, FUJITA Tomonori wrote: > > > On Thu, 4 Jun 2009 08:12:34 +0200 > > > Torsten Kaiser <just.for.lkml@xxxxxxxxxxxxxx> wrote: > > > > > >> On Thu, Jun 4, 2009 at 2:02 AM, FUJITA Tomonori > > >> <fujita.tomonori@xxxxxxxxxxxxx> wrote: > > >>> On Wed, 3 Jun 2009 21:30:32 +0200 > > >>> Torsten Kaiser <just.for.lkml@xxxxxxxxxxxxxx> wrote: > > >>>> Still happens with 2.6.30-rc8 (see trace at the end of the email) > > >>>> > > >>>> As orig_n_elem is only used two times in libata-core.c I suspected a > > >>>> corruption of the qc->sg, but adding checks for this did not trigger. > > >>>> So I looked into lib/dma-debug.c. > > >>>> It seems add_dma_entry() does not protect against adding the same > > >>>> entry twice. > > >>> Do you mean that add_dma_entry() doesn't protect against adding a new > > >>> entry identical to the existing entry, right? > > >> Yes, as I read the hash bucket code in lib/dma-debug.c a second entry > > >> from the same device and the same address will just be added to the > > >> list and on unmap it will always return the first entry. > > > > > > It means that two different DMA operations will be performed against > > > the same dma addresss on the same device at the same time. It doesn't > > > happen unless there is a bug in a driver, an IOMMU or somewhere, as I > > > wrote in the previous mail. > > > > > > > What about the draining buffers used by libata. Are they not the same buffer > > for all devices for all requests? > > I'm not sure if the drain buffer is used like that. But is there > easier ways to see the same buffer; e.g. sending the same buffer twice > with DIO? I'm pretty sure we discussed this some months ago, the intel iommu driver had a similar bug iirc. Lets say you want to write the same 4kb block to two spots on the disk. You prepare and submit that with O_DIRECT and using aio. On a device with NCQ, that could easily map the same page twice. Or, perhaps more likely, doing 512b writes and not getting all of them merged. > As I wrote, I assume that he uses GART IOMMU; it allocates an unique > dma address per dma mapping operation. > > However, dma-debug is broken wrt this, I guess. Seems so. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
