* Joerg Roedel <joerg.roedel@xxxxxxx> wrote: > > On Fri, Jun 05, 2009 at 05:33:14PM +0900, FUJITA Tomonori wrote: > > dma-debugs wrongly assumes that no multiple DMA transfers are > > performed against the same dma address on one device at the same > > time. However it's true only with hardware IOMMUs. For example, an > > application can easily send the same buffer twice with different > > lengths to one device by using DIO and AIO. If these requests are not > > unmapped in the same order in which they were mapped, > > hash_bucket_find() finds a wrong entry and gives a false warning. > > > > We should fix this before 2.6.30 release. Seems that there is no > > easy way to fix it. I think that it's better to just disable > > dma-debug for now. > > > > Torsten Kaiser found this bug with the RAID1 configuration: > > > > http://marc.info/?t=124336541900008&r=1&w=2 > > > > Argh, I never thought that this can happen. But its not explicitly > forbidden so we have to handle this situation. Thanks for tracking > down the bug to this issue. > > However, I think there is a somehow simple fix for the issue. > Patch is attached. Its the least intrusive way I can think of to > fix this problem. > > But its up to Linus/Ingo to decide if it can be accepted at this > very late point in the cycle. Since dma-debug is new with 2.6.30 > it will at least not introduce any regression. [...] I think it's too late for v2.6.30 to do any of the changes - and the DMA debug facility is off by default. Also, i think such DMA patterns, while 'allowed' can be quite dangerous as its such a rare usage combination really. AIO and DIO are crazy to begin with, mixing AIO and DIO for the same buffer is madness square two. (It can result in 3 agents for the same memory address: CPU, dma1 and dma2. How many interesting chipset erratums could there be related to such scenarios?) But it is certainly not the task of a debug facility to restrict existing user-visible ABIs, so fixing the false positive is correct. So i've applied your fix to the iommu branch for v2.6.31 and marked it for -stable backporting, that way 2.6.30.1 will be able to pick the patch up (if it remains problem-free in testing). Thanks, Ingo -- 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
