Drivers are allowed (actually have to) disable unrelated crtcs in their ->set_config callback (when we steal all the connectors from that crtc). If they do that they'll clear crtc->fb to NULL.
Which results in a refcount leak, since the drm core is keeping track of that reference.
To fix this track the old fb of all crtcs and adjust references for all of them. Of course, since we only hold an additional reference for the fb for the current crtc we need to increase refcounts before we drop the old one.
This approach has the benefit that it inches us a bit closer to an atomic modeset world, where we want to update the config of all crtcs in one step.
This regression has been introduce in the framebuffer refcount conversion, specifically in
commit b0d1232589df5575c5971224ac4cb30e7e525884 Author: Daniel Vetter daniel.vetter@ffwll.ch Date: Tue Dec 11 01:07:12 2012 +0100
drm: refcounting for crtc framebuffers
Reported-by: Russell King linux@arm.linux.org.uk Cc: Russell King linux@arm.linux.org.uk Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch --- drivers/gpu/drm/drm_crtc.c | 22 ++++++++++++++++------ include/drm/drm_crtc.h | 4 ++++ 2 files changed, 20 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c index bcee25a..3486a00 100644 --- a/drivers/gpu/drm/drm_crtc.c +++ b/drivers/gpu/drm/drm_crtc.c @@ -1931,21 +1931,31 @@ out: int drm_mode_set_config_internal(struct drm_mode_set *set) { struct drm_crtc *crtc = set->crtc; - struct drm_framebuffer *fb, *old_fb; + struct drm_framebuffer *fb; + struct drm_crtc *tmp; int ret;
- old_fb = crtc->fb; + /* + * NOTE: ->set_config can also disable other crtcs (if we steal all + * connectors from it), hence we need to refcount the fbs across all + * crtcs. Atomic modeset will have saner semantics ... + */ + list_for_each_entry(tmp, &crtc->dev->mode_config.crtc_list, head) + tmp->old_fb = tmp->fb; + fb = set->fb;
ret = crtc->funcs->set_config(set); if (ret == 0) { /* crtc->fb must be updated by ->set_config, enforces this. */ WARN_ON(fb != crtc->fb); + }
- if (old_fb) - drm_framebuffer_unreference(old_fb); - if (fb) - drm_framebuffer_reference(fb); + list_for_each_entry(tmp, &crtc->dev->mode_config.crtc_list, head) { + if (tmp->fb) + drm_framebuffer_reference(tmp->fb); + if (tmp->old_fb) + drm_framebuffer_unreference(tmp->old_fb); }
return ret; diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index 53c33e2..07d1dbbb 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -409,6 +409,10 @@ struct drm_crtc { /* framebuffer the connector is currently bound to */ struct drm_framebuffer *fb;
+ /* Temporary tracking of the old fb while a modeset is ongoing. Used + * by drm_mode_set_config_internal to implement correct refcounting. */ + struct drm_framebuffer *old_fb; + bool enabled;
/* Requested mode from modesetting. */