drm/fbdev: Return -EBUSY when oopsing

Trying to do anything with kms drivers when oopsing has become a
failing proposition. But since we can end up in the fbdev code simply
due to the console unblanking that's done unconditionally just
removing our panic handler isn't enough. We need to block all fbdev
callbacks when oopsing.

There was already one in the blank handler, but it failed silently.
That makes it impossible for drivers (like i915) who subclass these
functions to figure this out.

Instead consistently return -EBUSY so that everyone knows that we
really don't want to be bothered right now. This also allows us to
remove a pile of FIXMEs from the i915 fbdev code (since due to the
failure code they now won't attempt to grab dangerous locks any more).

Cc: Dave Airlie <airlied@gmail.com>
Cc: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/drm_fb_helper.c

@@ -490,14 +490,6 @@ static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
 	struct drm_connector *connector;
 	int i, j;
 
-	/*
-	 * fbdev->blank can be called from irq context in case of a panic.
-	 * Since we already have our own special panic handler which will
-	 * restore the fbdev console mode completely, just bail out early.
-	 */
-	if (oops_in_progress)
-		return;
-
 	/*
 	 * For each CRTC in this fb, turn the connectors on/off.
 	 */
@@ -531,6 +523,9 @@ static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
  */
 int drm_fb_helper_blank(int blank, struct fb_info *info)
 {
+	if (oops_in_progress)
+		return -EBUSY;
+
 	switch (blank) {
 	/* Display: On; HSync: On, VSync: On */
 	case FB_BLANK_UNBLANK:
@@ -978,9 +973,10 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
 	int i, j, rc = 0;
 	int start;
 
-	if (__drm_modeset_lock_all(dev, !!oops_in_progress)) {
+	if (oops_in_progress)
 		return -EBUSY;
-	}
+
+	drm_modeset_lock_all(dev);
 	if (!drm_fb_helper_is_bound(fb_helper)) {
 		drm_modeset_unlock_all(dev);
 		return -EBUSY;
@@ -1129,6 +1125,9 @@ int drm_fb_helper_set_par(struct fb_info *info)
 	struct drm_fb_helper *fb_helper = info->par;
 	struct fb_var_screeninfo *var = &info->var;
 
+	if (oops_in_progress)
+		return -EBUSY;
+
 	if (var->pixclock != 0) {
 		DRM_ERROR("PIXEL CLOCK SET\n");
 		return -EINVAL;
@@ -1154,9 +1153,10 @@ int drm_fb_helper_pan_display(struct fb_var_screeninfo *var,
 	int ret = 0;
 	int i;
 
-	if (__drm_modeset_lock_all(dev, !!oops_in_progress)) {
+	if (oops_in_progress)
 		return -EBUSY;
-	}
+
+	drm_modeset_lock_all(dev);
 	if (!drm_fb_helper_is_bound(fb_helper)) {
 		drm_modeset_unlock_all(dev);
 		return -EBUSY;

drivers/gpu/drm/i915/intel_fbdev.c

@@ -55,13 +55,6 @@ static int intel_fbdev_set_par(struct fb_info *info)
 	ret = drm_fb_helper_set_par(info);
 
 	if (ret == 0) {
-		/*
-		 * FIXME: fbdev presumes that all callbacks also work from
-		 * atomic contexts and relies on that for emergency oops
-		 * printing. KMS totally doesn't do that and the locking here is
-		 * by far not the only place this goes wrong.  Ignore this for
-		 * now until we solve this for real.
-		 */
 		mutex_lock(&fb_helper->dev->struct_mutex);
 		intel_fb_obj_invalidate(ifbdev->fb->obj, ORIGIN_GTT);
 		mutex_unlock(&fb_helper->dev->struct_mutex);
@@ -80,13 +73,6 @@ static int intel_fbdev_blank(int blank, struct fb_info *info)
 	ret = drm_fb_helper_blank(blank, info);
 
 	if (ret == 0) {
-		/*
-		 * FIXME: fbdev presumes that all callbacks also work from
-		 * atomic contexts and relies on that for emergency oops
-		 * printing. KMS totally doesn't do that and the locking here is
-		 * by far not the only place this goes wrong.  Ignore this for
-		 * now until we solve this for real.
-		 */
 		mutex_lock(&fb_helper->dev->struct_mutex);
 		intel_fb_obj_invalidate(ifbdev->fb->obj, ORIGIN_GTT);
 		mutex_unlock(&fb_helper->dev->struct_mutex);
@@ -106,13 +92,6 @@ static int intel_fbdev_pan_display(struct fb_var_screeninfo *var,
 	ret = drm_fb_helper_pan_display(var, info);
 
 	if (ret == 0) {
-		/*
-		 * FIXME: fbdev presumes that all callbacks also work from
-		 * atomic contexts and relies on that for emergency oops
-		 * printing. KMS totally doesn't do that and the locking here is
-		 * by far not the only place this goes wrong.  Ignore this for
-		 * now until we solve this for real.
-		 */
 		mutex_lock(&fb_helper->dev->struct_mutex);
 		intel_fb_obj_invalidate(ifbdev->fb->obj, ORIGIN_GTT);
 		mutex_unlock(&fb_helper->dev->struct_mutex);