On Sun, Dec 21, 2014 at 02:40:24PM +0000, Cheng, Yao wrote: > > -----Original Message----- > > From: Daniel Vetter [mailto:daniel.vetter@xxxxxxxx] > > Sent: Thursday, December 18, 2014 19:21 > > To: Thierry Reding > > Cc: Cheng, Yao; intel-gfx@xxxxxxxxxxxxxxxxxxxxx; dri- > > devel@xxxxxxxxxxxxxxxxxxxxx; 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 Thu, Dec 18, 2014 at 11:04 AM, Thierry Reding <thierry.reding@xxxxxxxxx> > > wrote: > > >> 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.). > > > > > > Yes, that's somewhat ugly, but I don't see a way around that. I'd also > > > think that moving platform_device_add() to a workqueue would be the > > > best option here. > > > > Or we simply kill drm_global_mutex for platform drivers that don't use the - > > >probe hook. It should work when they have a correct order betwen > > drm_dev_alloc and _register and all the code in between. So just ditch the - > > >load callback in teh ipvr driver and rework the load sequence as suggested > > somewhere else and this is fixed already. No need for bottom halfs I think. > > Daniel, sorry I didn't quite understand "platform drivers that don't use > the probe hook". For initialization, the ipvr platform driver's probe() > is called in following 2 possible paths: > 1. ipvr installed before i915. In this case, ipvr's probe() is called > inside i915_driver_load() and falls into the drm_global_mutex dead lock. > 2. i915 installed before ipvr. In this case, ipvr's probe() is called > without drm_global_mutex held by i915 and no dead lock issue. > If we kill drm_global_mutex, will path 2 run into issue? And in your > suggestion, how to rework the load sequence? Do you mean calling ipvr's > load() callback directly during platform driver probe()? Hm right it's not that simple really. What we need in more detail is: - Move the mutex_lock(&drm_global_mutex) out of drm_dev_register into all the callers. If a driver has a ->load() callback it most likely is racy with the usual load ordering issues. - Rework ipvr to no longer have a ->load callback. Insteaed use the following sequence (in the platform ->probe callback): drm_dev_alloc(); ipvr_load(); drm_dev_register(); With that ordering we don't need the additional guarantees that drm_global_mutex provides and we can avoid to take that lock around drm_dev_registrer() call in the ipvr code. This should resolve the deadlock I hope. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
