On Thu, Sep 12, 2013 at 05:36:43PM +0200, Daniel Vetter wrote: > The set_need_resched in i915_gem.c:i915_gem_fault can actually be > removed. It was there to give the error handler a chance to sneak in > and reset the hw/sw tracking when the gpu is dead. That hack goes back > to the days when the locking around our error handler was somewhere > between nonexistent and totally broken, nowadays we keep things from > live-locking by a bit of magic in i915_mutex_lock_interruptible. I'll > whip up a patch to rip this out. I'll also check that our testsuite > properly exercises this path (needs a bit of work on a quick look for > better coverage). > > The one in udl just looks like copypasta from i915, without any > justification (at least I don't see any) for why it's there. Probably > can die, too, since there isn't any gpu to reset on usb display-link > devices ... OK, awesome that. 2 down. > The one in ttm is just bonghits to shut up lockdep: ttm can recurse > into it's own pagefault handler and then deadlock, the trylock just > keeps lockdep quiet. We've had that bug arise in drm/i915 due to some > fun userspace did and now have testcases for them. The right solution > to fix this is to use copy_to|from_user_atomic in ttm everywhere it > holds locks and have slowpaths which drops locks, copies stuff into a > temp allocation and then continues. At least that's how we've fixed > all those inversions in i915-gem. I'm not volunteering to fix this ;-) Yikes.. so how common is it? If I simply rip the set_need_resched() out it will 'spin' on the fault a little longer until a 'natural' preemption point -- if such a thing is every going to happen. It would make that path take longer, but not be more or less broken. So if its a rare path, I'll just rip the set_need_resched() out and you DRM people can then fix up at your own pace. _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
