drm/i915/fbdev: Check for existence of ifbdev->vma before operations

Commit fabef825626d ("drm/i915: Drop struct_mutex around frontbuffer
flushes") adds a dependency to ifbdev->vma when flushing the framebufer,
but the checks are only against the existence of the ifbdev->fb and not
against ifbdev->vma. This leaves a window of opportunity where we may
try to operate on the fbdev prior to it being probed (thanks to
asynchronous booting).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101534
Fixes: fabef825626d ("drm/i915: Drop struct_mutex around frontbuffer flushes")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170622160211.783-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: stable@vger.kernel.org
(cherry picked from commit 15727ed0d944ce1dec8b9e1082dd3df29a0fdf44)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index 03347c6ae599..0c4cde6b2e6f 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -535,13 +535,14 @@ static void intel_fbdev_destroy(struct intel_fbdev *ifbdev)
 
         drm_fb_helper_fini(&ifbdev->helper);
 
-        if (ifbdev->fb) {
+        if (ifbdev->vma) {
                 mutex_lock(&ifbdev->helper.dev->struct_mutex);
                 intel_unpin_fb_vma(ifbdev->vma);
                 mutex_unlock(&ifbdev->helper.dev->struct_mutex);
+        }
 
+        if (ifbdev->fb)
                 drm_framebuffer_remove(&ifbdev->fb->base);
-        }
 
         kfree(ifbdev);
 }
@@ -765,7 +766,7 @@ void intel_fbdev_set_suspend(struct drm_device *dev, int state, bool synchronous
         struct intel_fbdev *ifbdev = dev_priv->fbdev;
         struct fb_info *info;
 
-        if (!ifbdev || !ifbdev->fb)
+        if (!ifbdev || !ifbdev->vma)
                 return;
 
         info = ifbdev->helper.fbdev;
@@ -812,7 +813,7 @@ void intel_fbdev_output_poll_changed(struct drm_device *dev)
 {
         struct intel_fbdev *ifbdev = to_i915(dev)->fbdev;
 
-        if (ifbdev && ifbdev->fb)
+        if (ifbdev && ifbdev->vma)
                 drm_fb_helper_hotplug_event(&ifbdev->helper);
 }
 
@@ -824,7 +825,7 @@ void intel_fbdev_restore_mode(struct drm_device *dev)
                 return;
 
         intel_fbdev_sync(ifbdev);
-        if (!ifbdev->fb)
+        if (!ifbdev->vma)
                 return;
 
         if (drm_fb_helper_restore_fbdev_mode_unlocked(&ifbdev->helper) == 0)