[PATCH] Revert "drm/core: Preserve the framebuffer after removing it."

[Hans de Goede]

This reverts commit 13803132818c ("drm/core: Preserve the framebuffer
after removing it.").

This commit assumes that going through drm_framebuffer_remove() is not
necessary because "the fbdev code or any system compositor should restore
the planes anyway so there's no need to do it twice". But this is not true
for secondary GPUs / slave outputs.

This revert fixes the dgpu no longer suspending on laptops with
switchable graphics after an external output which is connected
to the dgpu has been used.

And it fixes the WARN_ON to detect drm_framebuffer leaks in
drm_mode_config_cleanup() triggering when unplugging an USB displaylink
device; or when rmmod-ing the secondary GPU kms driver on laptops with
switchable-graphics.

Also this part of the reverted commit's commit-msg: "The old fb_id is
zero'd, so there's no danger of being able to restore the fb from fb_id."
is no longer true, the zero-ing does not happen until drm_framebuffer_free
gets called, which does not happen until the last ref is dropped, so
if a crtc's primary->fb is still pointing to this fb, the id will not
get zero'd and userspace could potentially gain access to the removed
fb again.

Cc: stable at vger.kenrel.org
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/drm_crtc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index e08f962..15f5cd7 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -3474,7 +3474,7 @@ int drm_mode_rmfb(struct drm_device *dev,
 	mutex_unlock(&dev->mode_config.fb_lock);
 	mutex_unlock(&file_priv->fbs_lock);
 
-	drm_framebuffer_unreference(fb);
+	drm_framebuffer_remove(fb);
 
 	return 0;
 
@@ -3656,8 +3656,8 @@ void drm_fb_release(struct drm_file *priv)
 	list_for_each_entry_safe(fb, tfb, &priv->fbs, filp_head) {
 		list_del_init(&fb->filp_head);
 
-		/* This drops the fpriv->fbs reference. */
-		drm_framebuffer_unreference(fb);
+		/* This will also drop the fpriv->fbs reference. */
+		drm_framebuffer_remove(fb);
 	}
 }
 
-- 
2.7.4