Re: [PATCH v2] drm/i915: Fix BUG in i915_gem.c when switch to console

From: Xi Ruoyao
Date: Thu Mar 12 2015 - 07:25:16 EST

On 03/12/2015 04:28 PM, Jani Nikula wrote:
On Thu, 12 Mar 2015, Xi Ruoyao <xry111@xxxxxxxxxxx> wrote:
In intel_crtc_page_flip, intel_display.c, the code changed the framebuffer
assigned to plane crtc->primary by

crtc->primary->fb = fb;

However, it forgot to change crtc->primary->state->fb. However, when we
switch to console, some kernel code will read crtc->primary->state->fb
to get the framebuffer assigned to crtc->primaty. Then a framebuffer
object can be unpinned twice and a kernel BUG will be produced in i915_gem.c.

So, update crtc->primary->state->fb in intel_display.c using
drm_atomic_set_fb_for_plane to fix the BUG.

Signed-off-by: Xi Ruoyao <xry111@xxxxxxxxxxx>
Fixed: Bug 93711 <>
Is this a problem with drm-intel-nightly? In particular see

commit afd65eb4cc0578a9c07d621acdb8a570e2782bf7
Author: Matt Roper <matthew.d.roper@xxxxxxxxx>
Date: Tue Feb 3 13:10:04 2015 -0800

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

Matt, do you think this fixes the described issue? Can we backport to
drm-intel-fixes (and v4.0)?


Sorry, the previous patch is mangled by email client, so I am re-sending it.

drivers/gpu/drm/i915/intel_display.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index e730789..97083fd 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -37,6 +37,7 @@
#include <drm/i915_drm.h>
#include "i915_drv.h"
#include "i915_trace.h"
+#include <drm/drm_atomic.h>
#include <drm/drm_atomic_helper.h>
#include <drm/drm_dp_helper.h>
#include <drm/drm_crtc_helper.h>
@@ -9816,6 +9817,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
crtc->primary->fb = fb;
+ drm_atomic_set_fb_for_plane(crtc->primary->state, fb);
work->pending_flip_obj = obj;

Thank you to read my patch.

Matt's patch is better than mine since it fixed more conditions causing the
unsynchronize of plane->fb and plane->fb. But unfortunately, it cannot be
applied to mainline kernel (Linux 4.0.0-rc3) directly.

I'll try to apply Matt's changes to the mainline kernel.
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