[PATCH] drm/locking: Allow NULL crtc in drm_modeset_legacy_acquire_ctx

[Daniel Vetter]

I've missed checking this and so didn't notice that there's a NULL
check missing. Since depending upon calling context the crtc might not
even be there (disable-me-harder does happen around planes, especially
in cleanup code) we need to dodge the oops and look at the global
acquire ctx.

v2: Actually fix the oops for real and don't just move it two lines
down. That requires that we pass a drm_device pointer for the cases
where crtc could be NULL.

Reported-by: "Jasper St. Pierre" <jstpierre at mecheye.net>
Cc: "Jasper St. Pierre" <jstpierre at mecheye.net>
Cc: Rob Clark <robdclark at gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/drm_atomic_helper.c | 12 ++++++++----
 drivers/gpu/drm/drm_modeset_lock.c  | 12 ++++++++----
 include/drm/drm_modeset_lock.h      |  3 ++-
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index ca839bd9bb0d..32c34b5d5f68 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1171,7 +1171,8 @@ int drm_atomic_helper_update_plane(struct drm_plane *plane,
 	if (!state)
 		return -ENOMEM;
 
-	state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc);
+	state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc,
+							    plane->dev);
 retry:
 	plane_state = drm_atomic_get_plane_state(state, plane);
 	if (IS_ERR(plane_state)) {
@@ -1239,7 +1240,8 @@ int drm_atomic_helper_disable_plane(struct drm_plane *plane)
 	if (!state)
 		return -ENOMEM;
 
-	state->acquire_ctx = drm_modeset_legacy_acquire_ctx(plane->crtc);
+	state->acquire_ctx = drm_modeset_legacy_acquire_ctx(plane->crtc,
+							    plane->dev);
 retry:
 	plane_state = drm_atomic_get_plane_state(state, plane);
 	if (IS_ERR(plane_state)) {
@@ -1391,7 +1393,8 @@ int drm_atomic_helper_set_config(struct drm_mode_set *set)
 	if (!state)
 		return -ENOMEM;
 
-	state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc);
+	state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc,
+							    crtc->dev);
 retry:
 	crtc_state = drm_atomic_get_crtc_state(state, crtc);
 	if (IS_ERR(crtc_state)) {
@@ -1676,7 +1679,8 @@ int drm_atomic_helper_page_flip(struct drm_crtc *crtc,
 	if (!state)
 		return -ENOMEM;
 
-	state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc);
+	state->acquire_ctx = drm_modeset_legacy_acquire_ctx(crtc,
+							    crtc->dev);
 retry:
 	crtc_state = drm_atomic_get_crtc_state(state, crtc);
 	if (IS_ERR(crtc_state)) {
diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index 474e4d12a2d8..655958d4f23e 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -200,21 +200,25 @@ EXPORT_SYMBOL(drm_modeset_lock_crtc);
 /**
  * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
  * @crtc: drm crtc
+ * @dev: device
  *
  * Legacy ioctl operations like cursor updates or page flips only have per-crtc
  * locking, and store the acquire ctx in the corresponding crtc. All other
  * legacy operations take all locks and use a global acquire context. This
  * function grabs the right one.
+ *
+ * Note that either @crtc or @dev can be NULL, but not both.
  */
 struct drm_modeset_acquire_ctx *
-drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
+drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc,
+			       struct drm_device *dev)
 {
-	if (crtc->acquire_ctx)
+	if (crtc && crtc->acquire_ctx)
 		return crtc->acquire_ctx;
 
-	WARN_ON(!crtc->dev->mode_config.acquire_ctx);
+	WARN_ON(!dev->mode_config.acquire_ctx);
 
-	return crtc->dev->mode_config.acquire_ctx;
+	return dev->mode_config.acquire_ctx;
 }
 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
 
diff --git a/include/drm/drm_modeset_lock.h b/include/drm/drm_modeset_lock.h
index 28931a23d96c..cdbfd822e52f 100644
--- a/include/drm/drm_modeset_lock.h
+++ b/include/drm/drm_modeset_lock.h
@@ -135,7 +135,8 @@ void drm_modeset_lock_crtc(struct drm_crtc *crtc);
 void drm_modeset_unlock_crtc(struct drm_crtc *crtc);
 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev);
 struct drm_modeset_acquire_ctx *
-drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc);
+drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc,
+			       struct drm_device *dev);
 
 int drm_modeset_lock_all_crtcs(struct drm_device *dev,
 		struct drm_modeset_acquire_ctx *ctx);
-- 
2.1.1