> -----Original Message----- > From: Daniel Vetter [mailto:daniel.vetter@xxxxxxxx] On Behalf Of Daniel > Vetter > Sent: Monday, November 24, 2014 21:15 > To: Thierry Reding > Cc: Daniel Vetter; Cheng, Yao; intel-gfx@xxxxxxxxxxxxxxxxxxxxx; dri- > devel@xxxxxxxxxxxxxxxxxxxxx; daniel.vetter@xxxxxxxx; Kelley, Sean V; Chehab, > John; emil.l.velikov@xxxxxxxxx; Jiang, Fei > Subject: Re: [RFC PATCH v3 4/4] tests/drv_module_reload: add ipvr support > > 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. 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? > -Daniel Thierry/Daniel, the actual symptom is, after "rmmod i915", though drm_drv_release() is also called on the child device "ipvr", I still see the module exist in the system (check it by "lsmod"). This causes issue when I modprobe i915 and ipvr again later. I don't understand why this happens but I believe what Daniel said: "grabbing a module refcount for the platform device doesn't work (it would pin the module forever)". > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
