On Friday, July 19, 2013 04:16:30 PM Greg Kroah-Hartman wrote: > On Fri, Jul 19, 2013 at 11:38:04PM +0200, Rafael J. Wysocki wrote: > > Alas, this is not the one I'd like to apply. > > > > With that patch applied, new device objects are created to avoid binding the > > processor driver directly to the cpu system device objects, because that > > apparently confuses udev and it starts to ignore the cpu modalias once the > > driver has been bound to any of those objects. > > > > I've verified in the meantime that this indeed is the case. > > > > A link to the patch in question: https://patchwork.kernel.org/patch/2830561/ > > > > Greg, I asked you some time ago whether or not it was possible for udev to > > stop > > autoloading modules that matched the cpu modalias after a driver had been > > bound > > to the cpu system device objects and you said "no". However, this time I > > can > > say with certainty that that really is the case. So, the question now is > > whether or not we can do anything in the kernel to avoid that confusion in > > udev > > instead of applying the patch linked above (which is beyond ugly in my not > > so > > humble opinion)? > > udev isn't doing any module loading, 'modprobe' is just being called for > any new module alias that shows up in the system, and all of the drivers > that match it then get loaded.
The problem is that that doesn't happen when a driver is bound to the cpu system device objects. modprobe is just not called for modules that match the cpu modalias in that case. If I call modprobe manually for any of the modules in question, it loads and works no problem. > How is it a problem if a module is attempted to be loaded that is > already loaded? How is it a problem if a different module is loaded for > a device already bound to a driver? Both of those should be total > "no-ops" for the kernel. Precisely, but that's not what happens in practice, hence my question. The situation is this: - With 3.11-rc1 modules that match the CPU modalias are not loaded automatically (that is, modprobe is not called for them by udev) after the processor module is loaded. - With 3.10 they are loaded automatically at any time. - With the patch at https://patchwork.kernel.org/patch/2830561/ on top of 3.11-rc1 the situation is the same as for 3.10. Therefore we have a kernel regression from 3.10 (with respect to the existing user space which is udev) in 3.11-rc1 3.10 and the patch at https://patchwork.kernel.org/patch/2830561/ makes that regression go away. However, that patch is totally voodoo programming, so I wonder if there is any saner alternative or we really need to do voodoo programming in the kernel to work around udev's confusion. > But, I don't know anything about the cpu code, how is loading a module > causing problems? That sounds like it needs to be fixes, as any root > user can load modules whenever they want, you can't protect the kernel > from doing that. Yes, that needs to be fixed, but I don't know *why* it is a problem in the first place. I'd like to understand what's going on, because I don't right now. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
