Commit 94284037 authored Sep 21, 2015 by Matt Roper Committed by Daniel Vetter Sep 24, 2015

drm/fbdev: Update legacy plane->fb refcounting for atomic restore



Starting with commit

        commit 28cc504e
        Author: Rob Clark <robdclark@gmail.com>
        Date:   Tue Aug 25 15:36:00 2015 -0400

            drm/i915: enable atomic fb-helper

I've been seeing some panics on i915 when the DRM master shuts down that appear
to be caused by using an already-freed framebuffer (i.e., we're unexpectedly
dropping our initial FB's reference count to 0 and freeing it, which causes a
crash when we try to restore it later).  Digging deeper, the state FB
refcounting is working as expected, but we seem to be missing proper
refcounting on the legacy plane->fb pointers in the new atomic fbdev code.

Tracking plane->old_fb and then doing a ref/unref at the end of the
fbdev restore like we do in the legacy ioctl's ensures we don't miscount
references on plane->fb and avoids the panics.

v2 from Daniel:

Really do what the atomic ioctl does:
- Also update plane->fb and plane->crtc.
- Clear out plane->old_fb on failures too.

v3: git add everything. Oops.

v4: Also clear old_fb in all other failure paths, spotted by David.

Cc: Rob Clark <robdclark@gmail.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com> (v1)
Reviewd-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

parent 5e7d4944

drivers/gpu/drm/drm_fb_helper.c

+18 −5

Original line number	Original line	Diff line number	Diff line
	@@ -352,6 +352,8 @@ retry:
	drm_for_each_plane(plane, dev) {		drm_for_each_plane(plane, dev) {
	struct drm_plane_state *plane_state;		struct drm_plane_state *plane_state;

			plane->old_fb = plane->fb;

	plane_state = drm_atomic_get_plane_state(state, plane);		plane_state = drm_atomic_get_plane_state(state, plane);
	if (IS_ERR(plane_state)) {		if (IS_ERR(plane_state)) {
	ret = PTR_ERR(plane_state);		ret = PTR_ERR(plane_state);
	@@ -382,15 +384,26 @@ retry:
	}		}

	ret = drm_atomic_commit(state);		ret = drm_atomic_commit(state);
	if (ret != 0)
	goto fail;

	return 0;

	fail:		fail:
			drm_for_each_plane(plane, dev) {
			if (ret == 0) {
			struct drm_framebuffer *new_fb = plane->state->fb;
			if (new_fb)
			drm_framebuffer_reference(new_fb);
			plane->fb = new_fb;
			plane->crtc = plane->state->crtc;

			if (plane->old_fb)
			drm_framebuffer_unreference(plane->old_fb);
			}
			plane->old_fb = NULL;
			}

	if (ret == -EDEADLK)		if (ret == -EDEADLK)
	goto backoff;		goto backoff;

			if (ret != 0)
	drm_atomic_state_free(state);		drm_atomic_state_free(state);

	return ret;		return ret;