Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference"

jmberg-intel · Ingo Molnar · commit f17b3ea3d2df · 2016-08-18T15:36:13.000+02:00
This reverts commit: fa7d81b ("drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference") As Peter explained: [...] lockless_dereference() is _stronger_ than READ_ONCE(), not weaker. [...] Also, clue is in the name: 'dereference', you don't actually dereference the pointer here, only load it. My next patch breaks the compile without this revert, because it assumes you want to deference and thus also need the struct type visible (which it isn't here), so revert it. Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Johannes Berg <johannes.berg@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1470909022-687-1-git-send-email-johannes@sipsolutions.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
@@ -464,7 +464,7 @@ static bool drm_fb_helper_is_bound(struct drm_fb_helper *fb_helper)
 
 	/* Sometimes user space wants everything disabled, so don't steal the
 	 * display if there's a master. */
-	if (lockless_dereference(dev->master))
+	if (READ_ONCE(dev->master))
 		return false;
 
 	drm_for_each_crtc(crtc, dev) {
