From 373701b1fc7d7c0013ae4fffd8103615c150751e Mon Sep 17 00:00:00 2001
From: Jani Nikula <jani.nikula@intel.com>
Date: Tue, 24 Nov 2015 21:21:55 +0200
Subject: [PATCH] drm: fix potential dangling else problems in for_each_ macros
Git-commit: 373701b1fc7d7c0013ae4fffd8103615c150751e
Patch-mainline: 4.5-rc1
References: bsc#991038

We have serious dangling else bugs waiting to happen in our for_each_
style macros with ifs. Consider, for example,

 #define drm_for_each_plane_mask(plane, dev, plane_mask) \
         list_for_each_entry((plane), &(dev)->mode_config.plane_list, head) \
                 if ((plane_mask) & (1 << drm_plane_index(plane)))

If this is used in context:

	if (condition)
		drm_for_each_plane_mask(plane, dev, plane_mask);
	else
		foo();

foo() will be called for each plane *not* in plane_mask, if condition
holds, and not at all if condition doesn't hold.

Fix this by reversing the conditions in the macros, and adding an else
branch for the "for each" block, so that other if/else blocks can't
interfere. Provide a "for_each_if" helper macro to make it easier to get
this right.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448392916-2281-1-git-send-email-jani.nikula@intel.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 include/drm/drmP.h       |    3 +++
 include/drm/drm_atomic.h |    6 +++---
 include/drm/drm_crtc.h   |    4 ++--
 3 files changed, 8 insertions(+), 5 deletions(-)

--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1136,4 +1136,7 @@ static __inline__ bool drm_can_sleep(voi
 	return true;
 }
 
+/* helper for handling conditionals in various for_each macros */
+#define for_each_if(condition) if (!(condition)) {} else
+
 #endif
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -149,7 +149,7 @@ int __must_check drm_atomic_async_commit
 	     ((connector) = (state)->connectors[__i],			\
 	     (connector_state) = (state)->connector_states[__i], 1); 	\
 	     (__i)++)							\
-		if (connector)
+		for_each_if (connector)
 
 #define for_each_crtc_in_state(state, crtc, crtc_state, __i)	\
 	for ((__i) = 0;						\
@@ -157,7 +157,7 @@ int __must_check drm_atomic_async_commit
 	     ((crtc) = (state)->crtcs[__i],			\
 	     (crtc_state) = (state)->crtc_states[__i], 1);	\
 	     (__i)++)						\
-		if (crtc_state)
+		for_each_if (crtc_state)
 
 #define for_each_plane_in_state(state, plane, plane_state, __i)		\
 	for ((__i) = 0;							\
@@ -165,7 +165,7 @@ int __must_check drm_atomic_async_commit
 	     ((plane) = (state)->planes[__i],				\
 	     (plane_state) = (state)->plane_states[__i], 1);		\
 	     (__i)++)							\
-		if (plane_state)
+		for_each_if (plane_state)
 static inline bool
 drm_atomic_crtc_needs_modeset(struct drm_crtc_state *state)
 {
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1166,7 +1166,7 @@ struct drm_mode_config {
  */
 #define drm_for_each_plane_mask(plane, dev, plane_mask) \
 	list_for_each_entry((plane), &(dev)->mode_config.plane_list, head) \
-		if ((plane_mask) & (1 << drm_plane_index(plane)))
+		for_each_if ((plane_mask) & (1 << drm_plane_index(plane)))
 
 
 #define obj_to_crtc(x) container_of(x, struct drm_crtc, base)
@@ -1543,7 +1543,7 @@ static inline struct drm_property *drm_p
 /* Plane list iterator for legacy (overlay only) planes. */
 #define drm_for_each_legacy_plane(plane, dev) \
 	list_for_each_entry(plane, &(dev)->mode_config.plane_list, head) \
-		if (plane->type == DRM_PLANE_TYPE_OVERLAY)
+		for_each_if (plane->type == DRM_PLANE_TYPE_OVERLAY)
 
 #define drm_for_each_plane(plane, dev) \
 	list_for_each_entry(plane, &(dev)->mode_config.plane_list, head)
