-----Original Message----- From: Thierry Reding [mailto:thierry.reding@gmail.com] Sent: Wednesday, December 17, 2014 16:13 To: Cheng, Yao Cc: Daniel Vetter; intel-gfx@lists.freedesktop.org; dri- devel@lists.freedesktop.org; daniel.vetter@ffwll.ch; Kelley, Sean V; Chehab, John; emil.l.velikov@gmail.com; Jiang, Fei Subject: Re: [RFC PATCH v3 4/4] tests/drv_module_reload: add ipvr support
Thanks Thiery for the suggestion, pls see my inline comments
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").
Which module? ipvr or i915?
The ipvr module still exist by checking "lsmod" after rmmod i915
This causes issue when I modprobe i915 and ipvr again later.
What issue are you seeing? If your driver can't deal with a situation where it's probed again after being removed then you have a bug.
I double checked the symptom and found it was a deadlock on drm_global_mutex. When i915_driver_load() registers the platform device while ipvr module is in the system, ipvr's probe() function tries to lock drm_global_mutex which was already held by i915. I think either of the following 2 actions need to be moved to a bottom half e.g. a work queue: platform_device_add () call in i915_ved.c (called during i915_driver_load()) drm_dev_register() call during ipvr's probe() Which one makes more sense? pls kindly advise (I personally prefer the former one.).
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)"
What I'd expect to happen is this:
# modprobe i915 i915 registers a platform devices # modprobe ipvr driver core probes ipvr device # modprobe -r i915 i915 removes the platform device (ipvr's ->remove() is called)
I guess if you don't do anything else, then indeed the ipvr module will stay around, but the above should work idempotently, that is you should be able to repeat it an unlimited number of times and nothing should break.
In fact you should be able to run the following in any permutation without causing a crash:
# modprobe i915 # modprobe ipvr # modprobe -r ipvr # modprobe -r i915
If any permutation results in a crash you have a bug.
I assume all the permutations will work after fixing the deadlock.
Thierry