On Mon, Aug 10, 2015 at 01:35:58PM +0200, Thierry Reding wrote: > On Thu, Jul 09, 2015 at 11:32:32PM +0200, Daniel Vetter wrote: > > Hi all, > > > > I wanted to take another look at struct_mutex usage in modern (gem) drivers and > > noticed that for a fair lot we're very to be completely struct_mutex free. > > > > This pile here is the the simple part, which mostly just removes code and > > mutex_lock/unlock calls. All the patches here are independent and can be merged > > in any order whatsoever. My plan is to send out a pull request for all those not > > picked up by driver maintainers in 2-3 weeks or so, assuming no one complains. > > > > Of course review & comments still very much welcome. > > > > The more tricky 2nd part of this (and that one's not yet done) is to rework the > > gem mmap handler to use the same kref_get_unless_zero trick as ttm. With that > > there's no core requirement to hold struct_mutex over the final unref, which > > means we can make that one lockless. I plan to add a gem_object_free_unlocked > > for all the drivers which don't have any need for this lock. > > > > Also there's a few more drivers which can be made struct_mutex free easily, I'll > > propably stitch together poc patches for those. > > There's a concurrency bug in Tegra DRM currently because we don't lock > accesses to drm_mm (I guess this demonstrates how badly we need better > testing...) and it seems like this is typically protected by the very > same struct_mutex that you're on a crusade to remove. If your goal is > to get rid of it for good, should we simply add a separate lock just > for the drm_mm? We don't have another one that would fit. Yes, please just add your own driver-private lock. The next struct_mutex crusade series will actually do exactly that, at least for simple cases like armada. With that changes most drivers don't care about struct_mutex any more in their ->gem_free_object hook and I plan to add a new ->gem_free_object_unlocked variant for all the drivers which don't have any residual usage of struct_mutex. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
