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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 20/09/2021 08:38, Jani Nikula wrote:
> On Mon, 20 Sep 2021, Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> wrote:
>> On 18/09/2021 00:38, Matthew Brost wrote:
>>> From: Hugh Dickins <hughd@google.com>
>>>
>>> 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@google.com>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> Reviewed-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>>    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;
>>>
>