On Mon, Feb 15, 2016 at 03:17:55PM +0100, Peter Zijlstra wrote: > On Mon, Feb 15, 2016 at 02:36:43PM +0200, Joonas Lahtinen wrote: > > Instead of implementing a custom locked reference counting, use lockref. > > > > Current implementation leads to a deadlock splat on Intel SKL platforms > > when lockdep debugging is enabled. > > > > This is due to few of CPUfreq drivers (including Intel P-state) having this; > > policy->rwsem is locked during driver initialization and the functions called > > during init that actually apply CPU limits use get_online_cpus (because they > > have other calling paths too), which will briefly lock cpu_hotplug.lock to > > increase cpu_hotplug.refcount. > > > > On later calling path, when doing a suspend, when cpu_hotplug_begin() is called > > in disable_nonboot_cpus(), callbacks to CPUfreq functions get called after, > > which will lock policy->rwsem and cpu_hotplug.lock is already held by > > cpu_hotplug_begin() and we do have a potential deadlock scenario reported by > > our CI system (though it is a very unlikely one). See the Bugzilla link for more > > details. > > I've been meaning to change the thing into a percpu-rwsem, I just > haven't had time to look into the lockdep splat that generated. I've thrown Joonas patch into a local topic branch to shut up the noise in our CI, and it seems to be effective at that (2 runs thus far). I'll drop this again once we have a proper solution (whatever it'll be) upstream. Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
