On Wed, 14 Aug 2013 13:54:53 -0700, Grant Grundler wrote: > On Wed, Aug 14, 2013 at 3:49 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote: > > On Thu, Aug 08, 2013 at 11:28:44AM -0700, Grant Grundler wrote: > >> I can't speak to the previous BUG_ON(). I believe the EADDRESSINUSE > >> failures could be either WARN_ON or BUG_ON. This condition is > >> clearly a bug in the generic IOMMU allocator and I think that's why > >> KyongHo Cho used BUG_ON. > >> > >> Handing out duplicate addresses will generally lead to some sort of > >> data corruption or other fault depending on how robust the underlying > >> device drivers are written. So my preference is a BUG_ON to > >> immediately flag this condition instead of hoping a device driver will > >> correctly handling the dma mapping failure (Some do, most currently > >> don't). > >> > >> WARN_ON() + return -EADDRESSINUSE would be a good alternative. > > > > Even if it is a real BUG condition, I don't think it is worth to stop > > execution at this point. It makes debugging harder and the system less > > reliable. I prefer to go with the WARN_ON and an error return value. > > I'm ok with WARN_ON and an error return value. This is "valid" > behavior. I expect this bug to never happen but if and when it does, > I want a clear symptom (e.g. WARN_ON) that it happened. > Ok. Finally, everyone thinks that WARN_ON() is OK. It will be helpful for the kernel code that uses iommu api. > My concern is that historically, drivers did not get an error return > value on failure: > ftp://193.166.3.4/pub/linux/kernel/v2.3/patch-html/patch-2.3.47/linux_Documentation_DMA-mapping.txt.html > > or later: > https://www.kernel.org/pub/linux/kernel/people/marcelo/linux-2.4/Documentation/DMA-mapping.txt > > And thus, some drivers don't check or attempt to handle mapping > failures based on this existing code. Here is a recent example: > http://comments.gmane.org/gmane.linux.network/272969 > > I hope very few or none of those exist since Neil Horman demonstrated > "dma debugging" can flag this behavior. > > Just for fun, I'll include this link : (apperently 2003 was a good > year for DMA talks :) > http://ols.fedoraproject.org/OLS/Reprints-2003/LinuxSymposium2003-2side.pdf > (three talks on DMA issues) > Thank you for the resources :) Those will be helpful for the guys with me. > thanks > grant -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
