[PATCH] drm/crtc-helper: skip locking checks in panicking path

[Sergei Antonov]

Hello!
Below is my patch for drm. Here is a photo of kernel output I had:
http://s17.postimg.org/k0301hgf3/Untitled.jpg
to illustrate what I am writing in the description.

---
Subject: [PATCH] drm/crtc-helper: skip locking checks in panicking path

Skip locking checks in drm_helper_*_in_use() if they are called in panicking
path. See similar code in drm_warn_on_modeset_not_all_locked().

After panic information has been output, these WARN_ONs go off outputing a lot
of lines and scrolling the panic information out of the screen. Here is a
partial call trace showing how execution reaches them:

? drm_helper_crtc_in_use()
? __drm_helper_disable_unused_functions()
? several *_set_config functions
? drm_fb_helper_restore_fbdev_mode()

Cc: Dave Airlie <airlied at redhat.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Sergei Antonov <saproj at gmail.com>
---
 drivers/gpu/drm/drm_crtc_helper.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index df281b5..872ba11 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -29,6 +29,7 @@
  *      Jesse Barnes <jesse.barnes at intel.com>
  */
 
+#include <linux/kernel.h>
 #include <linux/export.h>
 #include <linux/moduleparam.h>
 
@@ -88,7 +89,13 @@ bool drm_helper_encoder_in_use(struct drm_encoder *encoder)
 	struct drm_connector *connector;
 	struct drm_device *dev = encoder->dev;
 
-	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
+	/*
+	 * We can expect this mutex to be locked if we are not panicking.
+	 * Locking is currently fubar in the panic handler.
+	 */
+	if (!oops_in_progress)
+		WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
+
 	list_for_each_entry(connector, &dev->mode_config.connector_list, head)
 		if (connector->encoder == encoder)
 			return true;
@@ -112,7 +119,13 @@ bool drm_helper_crtc_in_use(struct drm_crtc *crtc)
 	struct drm_encoder *encoder;
 	struct drm_device *dev = crtc->dev;
 
-	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
+	/*
+	 * We can expect this mutex to be locked if we are not panicking.
+	 * Locking is currently fubar in the panic handler.
+	 */
+	if (!oops_in_progress)
+		WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
+
 	list_for_each_entry(encoder, &dev->mode_config.encoder_list, head)
 		if (encoder->crtc == crtc && drm_helper_encoder_in_use(encoder))
 			return true;
-- 
1.9.0