[PATCH 3/5] drm/i915: Don't try to reference the fb in get_initial_plane_config()

Damien Lespiau
2015-02-05T17:22:24Z

Tvrtko noticed a new warning on boot:

WARNING: CPU: 1 PID: 353 at include/linux/kref.h:47 drm_framebuffer_reference+0x6c/0x80 [drm]()
Call Trace:
[<ffffffff8161f10c>] dump_stack+0x4f/0x7b
[<ffffffff81052caa>] warn_slowpath_common+0xaa/0xd0
[<ffffffff81052d8a>] warn_slowpath_null+0x1a/0x20
[<ffffffffa00d035c>] drm_framebuffer_reference+0x6c/0x80 [drm]
[<ffffffffa01c0df7>] update_state_fb.isra.54+0x47/0x50 [i915]
[<ffffffffa01ccd5c>] skylake_get_initial_plane_config+0x93c/0x950 [i915]
[<ffffffffa01e8721>] intel_modeset_init+0x1551/0x17c0 [i915]
[<ffffffffa02476e0>] i915_driver_load+0xed0/0x11e0 [i915]
[<ffffffff81627aa1>] ? _raw_spin_unlock_irqrestore+0x51/0x70
[<ffffffffa00ca8b7>] drm_dev_register+0x77/0x110 [drm]
[<ffffffffa00cda3b>] drm_get_pci_dev+0x11b/0x1f0 [drm]
[<ffffffff81098e3d>] ? trace_hardirqs_on+0xd/0x10
[<ffffffff81627aa1>] ? _raw_spin_unlock_irqrestore+0x51/0x70
[<ffffffffa0145276>] i915_pci_probe+0x56/0x60 [i915]
[<ffffffff813ad59c>] pci_device_probe+0x7c/0x100
[<ffffffff81466aad>] driver_probe_device+0x16d/0x380

We cannot take a reference at this point, not before
intel_framebuffer_init() and the underlying drm_framebuffer_init().

Introduced in:

commit 706dc7b549175e47f23e913b7f1e52874a7d0f56
Author: Matt Roper <matthew.d.roper@intel.com>
Date: Tue Feb 3 13:10:04 2015 -0800

drm/i915: Ensure plane->state->fb stays in sync with plane->fb

Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
---
drivers/gpu/drm/i915/intel_display.c | 35 +++++++++++++++++------------------
1 file changed, 17 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3301b61..e1e89d0 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2364,6 +2364,20 @@ static int skl_format_to_fourcc(int format, bool rgb_order, bool alpha)
}
}

+/* Update plane->state->fb to match plane->fb after driver-internal updates */
+static void
+update_state_fb(struct drm_plane *plane)
+{
+ if (plane->fb == plane->state->fb)
+ return;
+
+ if (plane->state->fb)
+ drm_framebuffer_unreference(plane->state->fb);
+ plane->state->fb = plane->fb;
+ if (plane->state->fb)
+ drm_framebuffer_reference(plane->state->fb);
+}
+
static bool
intel_alloc_plane_obj(struct intel_crtc *crtc,
struct intel_initial_plane_config *plane_config)
@@ -2411,20 +2425,6 @@ out_unref_obj:
return false;
}

-/* Update plane->state->fb to match plane->fb after driver-internal updates */
-static void
-update_state_fb(struct drm_plane *plane)
-{
- if (plane->fb == plane->state->fb)
- return;
-
- if (plane->state->fb)
- drm_framebuffer_unreference(plane->state->fb);
- plane->state->fb = plane->fb;
- if (plane->state->fb)
- drm_framebuffer_reference(plane->state->fb);
-}
-
static void
intel_find_plane_obj(struct intel_crtc *intel_crtc,
struct intel_initial_plane_config *plane_config)
@@ -2438,8 +2438,10 @@ intel_find_plane_obj(struct intel_crtc *intel_crtc,
if (!intel_crtc->base.primary->fb)
return;

- if (intel_alloc_plane_obj(intel_crtc, plane_config))
+ if (intel_alloc_plane_obj(intel_crtc, plane_config)) {
+ update_state_fb(intel_crtc->base.primary);
return;
+ }

kfree(intel_crtc->base.primary->fb);
intel_crtc->base.primary->fb = NULL;
@@ -6652,7 +6654,6 @@ i9xx_get_initial_plane_config(struct intel_crtc *crtc,
plane_config->size);

crtc->base.primary->fb = fb;
- update_state_fb(crtc->base.primary);
}

static void chv_crtc_clock_get(struct intel_crtc *crtc,
@@ -7690,7 +7691,6 @@ skylake_get_initial_plane_config(struct intel_crtc *crtc,
plane_config->size);

crtc->base.primary->fb = fb;
- update_state_fb(crtc->base.primary);
return;

error:
@@ -7782,7 +7782,6 @@ ironlake_get_initial_plane_config(struct intel_crtc *crtc,
plane_config->size);

crtc->base.primary->fb = fb;
- update_state_fb(crtc->base.primary);
}

static bool ironlake_get_pipe_config(struct intel_crtc *crtc,