drm: i915+fb: crtc->lock recursive locking deadlock on VT switch [>= 3.9-rc1 regresion]

[Chris Wilson]

On Sat, Apr 13, 2013 at 05:41:46PM +0200, Krzysztof Mazur wrote:
> Hi,
> 
> the drm_fb_helper_hotplug_event() locks all crtc->mutex locks by calling
> drm_modeset_lock_all() and later calls drm_fb_helper_probe_connector_modes(),
> which in case of i915 DRM driver effectively calls
> intel_get_load_detect_pipe() that tries to lock crtc->mutex again.
> This causes a deadlock, and can be in some cases triggered by VT
> switch to framebuffer console on i915.
> 
> This bug is introduced in Linux 3.9-rc1 and still exists
> in v3.9-rc6-183-gbf81710. Linux 3.8 is ok.

In Dave's drm-fixes branch:

commit 89ced125472b8551c65526934b7f6c733a6864fa
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Thu Apr 11 14:26:55 2013 +0000

    drm/fb-helper: Fix locking in drm_fb_helper_hotplug_event
    
    Driver's and ->fill_modes functions are allowed to grab crtc mutexes
    (for e.g. load detect). Hence we need to first only grab the general
    kms mutex, and only in a second step grab all locks to do the
    modesets.
    
    This prevents a deadlock on my gm45 in the tv load detect code called
    by drm_helper_probe_single_connector_modes.
    
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
    Signed-off-by: Dave Airlie <airlied at redhat.com>

-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre