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). -Chris -- Chris Wilson, Intel Open Source Technology Centre
