From: Matt Roper <matthew.d.roper@xxxxxxxxx>
Starting with commit
commit 28cc504e8d52248962f5b485bdc65f539e3fe21d
Author: Rob Clark <robdclark@xxxxxxxxx>
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.
Cc: Rob Clark <robdclark@xxxxxxxxx>
Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
drivers/gpu/drm/drm_fb_helper.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 64fc5ca8fda2..1b564a69f561 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -352,6 +352,8 @@ retry:
drm_for_each_plane(plane, dev) {
struct drm_plane_state *plane_state;
+ plane->old_fb = plane->fb;
+
plane_state = drm_atomic_get_plane_state(state, plane);
if (IS_ERR(plane_state)) {
ret = PTR_ERR(plane_state);
@@ -382,6 +384,20 @@ retry:
}
ret = drm_atomic_commit(state);
+
+ 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);
+ }
+ }
+
if (ret != 0)
goto fail;
--
2.5.1
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