On Mon, Nov 24, 2014 at 02:14:48PM +0100, Daniel Vetter wrote: > On Mon, Nov 24, 2014 at 10:55:46AM +0100, Thierry Reding wrote: > > On Fri, Nov 21, 2014 at 09:36:33PM +0100, Daniel Vetter wrote: > > > On Fri, Nov 21, 2014 at 09:27:04PM +0100, Thierry Reding wrote: > > > > On Sat, Nov 22, 2014 at 03:10:01AM +0800, Yao Cheng wrote: > > > > > on vlv, if ipvr is installed, it need be manually unloaded before > > > > > i915, otherwise user might run into use-after-free issue. > > > > > > > > Huh? That doesn't sound right. What exactly is it that's going wrong? > > > > You should never have to do this. If you do you're almost certainly > > > > doing something wrong in the kernel module. > > > > > > It's the hilarity called platform devices. Removing them is somewhat racy, > > > so doing that upfront makes the entire thing a bit safer. The use after > > > free is on the text, since grabbing a module refcount for the platform > > > device doesn't work (it would pin the module forever). > > > > I don't understand what the issue is here. I've used platform devices > > quite extensively on ARM and I've never encountered a situation where > > they were insufficient (or racy for that matter). > > > > If I understand correctly what this commit tries to achieve, then it > > unloads one module before another module that it depends on so that the > > dependency can be removed subsequently without causing a crash. That > > sounds really brittle to me. How are you going to document this for > > users so that they don't accidentally go and unload the i915 module and > > crash their system? > > Module unloading taints your kernel and isn't an end-user supported > feature. That simple ;-) > > Also afaik the problem is that you actually can't unload i915 until you've > unloaded the subordinate driver, since i915 registering the platform > driver prevents unload. That doesn't sound at all like use-after-free, so if that's really the only problem then the commit description should be more accurate. > Or at least that was my understanding, I didn't test this myself. I > just asked whether the unload script still works and apparently it > breaks. > > I guess what's different with ARM is that DT creates all the platform > devices, and not modules themselves? No, I don't think that has anything to do with it. I'm pretty sure I've seen this work reliably with something like MFD where one module can create a number of platform devices, and remove them again, just as well. Thierry
Attachment:
pgpTMPEzkVVzD.pgp
Description: PGP signature
_______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
