[0880/1094] drm: Try to acquire modeset lock on panic or sysrq

Commit Message

Dheeraj Jamwal Oct. 21, 2014, 10:58 a.m. UTC

From: Thierry Reding <[e-mail]>

Commit 62ff94a54921 "drm/crtc-helper: remove LOCKING from kerneldoc"
causes drm_helper_crtc_in_use() and drm_helper_encoder_in_use() to
complain loudly during a kernel panic or sysrq processing. This is
caused by nobody acquiring the modeset lock in these code paths.

This patch fixes this by trying to acquire the modeset lock for each
FB helper that's forced to kernel mode. If the lock can't be acquired,
it's likely that somebody else is performing a modeset. However, doing
another modeset concurrently might make things even worse, so the safe
option is to simply bail out in that case.

Reviewed-by: Daniel Vetter <[e-mail]>
Reviewed-by: David Herrmann <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
(cherry picked from commit b77f0765fdfb3a115e40effd890acb4674dc0989)

Signed-off-by: Dheeraj Jamwal <[e-mail]>
---
 drivers/gpu/drm/drm_fb_helper.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

Patch

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index a634a6b..f915837 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -326,12 +326,21 @@  static bool drm_fb_helper_force_kernel_mode(void)
 		return false;
 
 	list_for_each_entry(helper, &kernel_fb_helper_list, kernel_fb_list) {
-		if (helper->dev->switch_power_state == DRM_SWITCH_POWER_OFF)
+		struct drm_device *dev = helper->dev;
+
+		if (dev->switch_power_state == DRM_SWITCH_POWER_OFF)
+			continue;
+
+		if (!mutex_trylock(&dev->mode_config.mutex)) {
+			error = true;
 			continue;
+		}
 
 		ret = drm_fb_helper_restore_fbdev_mode(helper);
 		if (ret)
 			error = true;
+
+		mutex_unlock(&dev->mode_config.mutex);
 	}
 	return error;
 }