[Intel-gfx] [PATCH] drm/i915: use kref_put_mutex in i915_gem_request_unreference__unlocked

[Daniel Vetter]

On Tue, Apr 07, 2015 at 03:51:44PM +0200, Maarten Lankhorst wrote:
> Op 07-04-15 om 15:37 schreef Daniel Vetter:
> > On Tue, Apr 07, 2015 at 11:32:02AM +0200, Maarten Lankhorst wrote:
> >> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> >> ---
> >> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> >> index b13c5526a73b..7aaf8eddf19c 100644
> >> --- a/drivers/gpu/drm/i915/i915_drv.h
> >> +++ b/drivers/gpu/drm/i915/i915_drv.h
> >> @@ -2146,14 +2146,14 @@ i915_gem_request_unreference(struct drm_i915_gem_request *req)
> >>  static inline void
> >>  i915_gem_request_unreference__unlocked(struct drm_i915_gem_request *req)
> >>  {
> >> -	if (req && !atomic_add_unless(&req->ref.refcount, -1, 1)) {
> >> -		struct drm_device *dev = req->ring->dev;
> >> +	struct drm_device *dev;
> >> +
> >> +	if (!req)
> >> +		return;
> >>  
> >> -		mutex_lock(&dev->struct_mutex);
> >> -		if (likely(atomic_dec_and_test(&req->ref.refcount)))
> >> -			i915_gem_request_free(&req->ref);
> >> +	dev = req->ring->dev;
> >> +	if (kref_put_mutex(&req->ref, i915_gem_request_free, &dev->struct_mutex))
> >>  		mutex_unlock(&dev->struct_mutex);
> > We don't need this conditional unlock here since that's only possible if
> > you have a weak reference somewhere (i.e. using kref_get_unless_zero). If
> > the object only has strong references and you're dropping the last one it
> > can't magically get resurrected somehow.
> Because we use the same put call for kref_put and kref_put_mutex we do need to unlock struct_mutex here,
> kref_put_mutex doesn't release the mutex if true, so either the release call needs to do it or the callee.

Indeed I didn't realize that all existing users of kref_put_mutex unlock
the mutex in the free callback. So looks all good, so applied it.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch