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.
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;
>>
--
Jani Nikula, Intel Open Source Graphics Center
