[Intel-gfx] [PATCH] drm/i915: Move drm_framebuffer_unreference out of struct_mutex for takeover

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

intel_user_framebuffer_destroy() requires the struct_mutex for its
object bookkeeping, so this means that all calls to
drm_framebuffer_unreference must be held without that lock.

This is a simplified version of the identically named patch by Chris Wilson.

References: https://bugs.freedesktop.org/show_bug.cgi?id=89166
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index cb50854..0788507 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -14020,11 +14020,21 @@ void intel_modeset_gem_init(struct drm_device *dev)
 					       c->primary->fb,
 					       c->primary->state,
 					       NULL)) {
+			/*
+			 * We must drop struct_mutex when calling
+			 * drm_framebuffer_unreference and it is safe to do so
+			 * because it is not needed at this point anyway.
+			 * At this stage the driver is still single-threaded and
+			 * we are taking it only to silence a warning in
+			 * intel_pin_and_fence_fb_obj.
+			 */
+			mutex_unlock(&dev->struct_mutex);
 			DRM_ERROR("failed to pin boot fb on pipe %d\n",
 				  to_intel_crtc(c)->pipe);
 			drm_framebuffer_unreference(c->primary->fb);
 			c->primary->fb = NULL;
 			update_state_fb(c->primary);
+			mutex_lock(&dev->struct_mutex);
 		}
 	}
 	mutex_unlock(&dev->struct_mutex);
-- 
2.3.2