Re: 5.15-rc1 i915 blank screen booting on ThinkPads

[Matthew Brost <matthew.brost@intel.com>]

On Sat, Sep 18, 2021 at 01:52:48AM +0300, Jani Nikula wrote:
> On Fri, 17 Sep 2021, Matthew Brost <matthew.brost@intel.com> wrote:
> > On Fri, Sep 17, 2021 at 02:26:48PM -0700, Hugh Dickins wrote:
> >> On Thu, 16 Sep 2021, Jani Nikula wrote:
> >> > On Thu, 16 Sep 2021, Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> wrote:
> >> > > On 16/09/2021 05:37, Hugh Dickins wrote:
> >> > >> Two Lenovo ThinkPads, old T420s (2011), newer X1 Carbon 5th gen (2017):
> >> > >> i915 working fine on both up to 5.14, but blank screens booting 5.15-rc1,
> >> > >> kernel crashed in some way.
> >> ...
> >> > > Kernel logs with drm.debug=0xe, with the broken black screen state, 
> >> > > would probably answer a lot of questions if you could gather it from 
> >> > > both machines?
> >> > 
> >> > And for that, I think it's best to file separate bugs at [1] and attach
> >> > the logs there. It helps keep the info in one place. Thanks.
> >> > 
> >> > BR,
> >> > Jani.
> >> > 
> >> > [1] https://gitlab.freedesktop.org/drm/intel/issues/new
> >> 
> >> Thanks for the quick replies: but of course, getting kernel logs was
> >> the difficult part, this being bootup, with just a blank screen, and
> >> no logging to disk at this stage.  I've never needed it before, but
> >> netconsole to the rescue.
> >> 
> >> Problem then obvious, both machines now working,
> >> please let me skip the bug reports, here's a patch:
> >> 
> >
> > Thanks for finding / fixing this Hugh. I will post this patch in a way
> > our CI system can understand.
> 
> Thanks indeed!
> 
> Matt, please get rid of the BUG_ON while at it, and make it a
> WARN. Oopsing doesn't do anyone any good.
> 

Sure. Will do. Long term we should just look to rip out crap this (i.e.
stealing bits from aligned addresses for flags).

Matt

> BR,
> Jani.
> 
> >
> > Matt 
> >
> >> [PATCH] drm/i915: fix blank screen booting crashes
> >> 
> >> 5.15-rc1 crashes with blank screen when booting up on two ThinkPads
> >> using i915.  Bisections converge convincingly, but arrive at different
> >> and surprising "culprits", none of them the actual culprit.
> >> 
> >> netconsole (with init_netconsole() hacked to call i915_init() when
> >> logging has started, instead of by module_init()) tells the story:
> >> 
> >> kernel BUG at drivers/gpu/drm/i915/i915_sw_fence.c:245!
> >> with RSI: ffffffff814d408b pointing to sw_fence_dummy_notify().
> >> I've been building with CONFIG_CC_OPTIMIZE_FOR_SIZE=y, and that
> >> function needs to be 4-byte aligned.
> >> 
> >> Fixes: 62eaf0ae217d ("drm/i915/guc: Support request cancellation")
> >> Signed-off-by: Hugh Dickins <hughd@google.com>
> >> ---
> >> 
> >>  drivers/gpu/drm/i915/gt/intel_context.c |    1 +
> >>  1 file changed, 1 insertion(+)
> >> 
> >> --- a/drivers/gpu/drm/i915/gt/intel_context.c
> >> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> >> @@ -362,6 +362,7 @@ static int __intel_context_active(struct
> >>  	return 0;
> >>  }
> >>  
> >> +__aligned(4)	/* Respect the I915_SW_FENCE_MASK */
> >>  static int sw_fence_dummy_notify(struct i915_sw_fence *sf,
> >>  				 enum i915_sw_fence_notify state)
> >>  {
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center