On Mon, Aug 10, 2015 at 12:53:23PM +0100, Chris Wilson wrote: > 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. > > Actually that is one of the first targets for more fine-grained locking. > I would not add a new lock to drm_mm as at least for i915, we want to use > a similar per-vm lock (of which the drm_mm is just one part). Sorry if I was being unclear. I wasn't suggesting adding the lock to struct drm_mm, but rather add a driver-specific one specifically to serialize accesses to the drm_mm. I agree that it's better to do this in a driver-specific way because other structures may need to be protected by the same lock. Thierry
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