Re: [Intel-gfx] [PATCH] drm/i915: fix blank screen booting crashes

[Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>]

On 20/09/2021 08:38, Jani Nikula wrote:
> On Mon, 20 Sep 2021, Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
> > On 18/09/2021 00:38, Matthew Brost wrote:
> > > From: Hugh Dickins <hughd@xxxxxxxxxx>
> > >
> > > 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.
> >
> > It is certainly surprising this patch crashed SNB and KBL.
> >
> > How feasible would it be to make this code just not run when GuC is not
> > used? Given the field it adds is called ce->guc_blocked it sounds like a
> > natural and preferable thing to do... if possible.
> >
> > > 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.
> > >
> > > v2:
> > >    (Jani Nikula)
> > >     - Change BUG_ON to WARN_ON
> >
> > However in this case the code would then go on and call into a wrong
> > function offset which may be worse than a BUG_ON, no?
>
> So how about just
>
> if (WARN_ON(...))
> 	return;
>
> or whatever is needed to give both the user and the CI a better
> opportunity to see the error.

Sounds good to me.

Regards,

Tvrtko


> BR,
> Jani
>
>
> > > Fixes: 62eaf0ae217d ("drm/i915/guc: Support request cancellation")
> > > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> > > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> > > Reviewed-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> > > ---
> > >    drivers/gpu/drm/i915/gt/intel_context.c | 1 +
> > >    drivers/gpu/drm/i915/i915_sw_fence.c    | 4 +++-
> > >    2 files changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> > > index ff637147b1a9..f02c2202da9d 100644
> > > --- 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 i915_active *active)
> > >    	return 0;
> > >    }
> > >    
> > > +__aligned(4)	/* Respect the I915_SW_FENCE_MASK */
> >
> > Hugh suggested __i915_sw_fence_call which I think would be the right
> > thing to do.
> >
> > Regards,
> >
> > Tvrtko
> >
> > >    static int sw_fence_dummy_notify(struct i915_sw_fence *sf,
> > >    				 enum i915_sw_fence_notify state)
> > >    {
> > > diff --git a/drivers/gpu/drm/i915/i915_sw_fence.c b/drivers/gpu/drm/i915/i915_sw_fence.c
> > > index c589a681da77..1217b124c1d0 100644
> > > --- a/drivers/gpu/drm/i915/i915_sw_fence.c
> > > +++ b/drivers/gpu/drm/i915/i915_sw_fence.c
> > > @@ -14,8 +14,10 @@
> > >    
> > >    #if IS_ENABLED(CONFIG_DRM_I915_DEBUG)
> > >    #define I915_SW_FENCE_BUG_ON(expr) BUG_ON(expr)
> > > +#define I915_SW_FENCE_WARN_ON(expr) WARN_ON(expr)
> > >    #else
> > >    #define I915_SW_FENCE_BUG_ON(expr) BUILD_BUG_ON_INVALID(expr)
> > > +#define I915_SW_FENCE_WARN_ON(expr) BUILD_BUG_ON_INVALID(expr)
> > >    #endif
> > >    
> > >    static DEFINE_SPINLOCK(i915_sw_fence_lock);
> > > @@ -242,7 +244,7 @@ void __i915_sw_fence_init(struct i915_sw_fence *fence,
> > >    			  const char *name,
> > >    			  struct lock_class_key *key)
> > >    {
> > > -	BUG_ON(!fn || (unsigned long)fn & ~I915_SW_FENCE_MASK);
> > > +	I915_SW_FENCE_WARN_ON(!fn || (unsigned long)fn & ~I915_SW_FENCE_MASK);
> > >    
> > >    	__init_waitqueue_head(&fence->wait, name, key);
> > >    	fence->flags = (unsigned long)fn;