From: Matt Roper matthew.d.roper@intel.com
commit 7118fd9bd975a9f3093239d4c0f4e15356b57fab upstream.
pan_display_atomic() calls drm_atomic_clean_old_fb() to sanitize the legacy FB fields (plane->fb and plane->old_fb). However it was building the plane mask to pass to this function incorrectly (the bitwise OR was using plane indices rather than plane masks). The end result was that sometimes the legacy pointers would become out of sync with the atomic pointers. If another operation tried to re-set the same FB onto the plane, we might end up with the pointers back in sync, but improper reference counts, which would eventually lead to system crashes when we accessed a pointer to a prematurely-destroyed FB.
The cause here was a very subtle bug introduced in commit:
commit 07d3bad6c1210bd21e85d084807ef4ee4ac43a78 Author: Maarten Lankhorst maarten.lankhorst@linux.intel.com Date: Wed Nov 11 11:29:11 2015 +0100
drm/core: Fix old_fb handling in pan_display_atomic.
I found the crashes were most easily reproduced (on i915 at least) by starting X and then VT switching to a VT that wasn't running a console instance...the sequence of vt/fbcon entries that happen in that case trigger a reference count mismatch and crash the system.
Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93313 Signed-off-by: Matt Roper matthew.d.roper@intel.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Xuebing Chen chenxb_99091@126.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/gpu/drm/drm_fb_helper.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -1256,7 +1256,7 @@ retry: goto fail;
plane = mode_set->crtc->primary; - plane_mask |= drm_plane_index(plane); + plane_mask |= (1 << drm_plane_index(plane)); plane->old_fb = plane->fb; }