[PATCH 5/9] drm/i915: More surgically unbreak the modeset vs reset deadlock

[Daniel Vetter]

On Wed, Jul 19, 2017 at 4:05 PM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> On Wed, Jul 19, 2017 at 3:42 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>> Quoting Daniel Vetter (2017-07-19 13:54:58)
>>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>>> index 5aa7ca1ab592..4762f158032d 100644
>>> --- a/drivers/gpu/drm/i915/intel_display.c
>>> +++ b/drivers/gpu/drm/i915/intel_display.c
>>> @@ -3471,10 +3471,9 @@ void intel_prepare_reset(struct drm_i915_private *dev_priv)
>>>             !gpu_reset_clobbers_display(dev_priv))
>>>                 return;
>>>
>>> -       /* We have a modeset vs reset deadlock, defensively unbreak it.
>>> -        *
>>> -        * FIXME: We can do a _lot_ better, this is just a first iteration.*/
>>> -       i915_gem_set_wedged(dev_priv);
>>> +       /* We have a modeset vs reset deadlock, defensively unbreak it. */
>>> +       set_bit(I915_RESET_MODESET, &dev_priv->gpu_error.flags);
>>> +       wake_up_all(&dev_priv->gpu_error.wait_queue);
>>
>> How are we breaking the
>>
>>         modeset_lock -> struct_mutex -> wait_on_reset ?
>>
>> We wait the modeset_lock next which stops the reset from
>> proceeding, and so the deadlock persists until the wedge-me timeout?
>
> Hm indeed, I didn't check my logs carefully enough and there's still
> "i915_reset_device timed out" in it. But I also thought the only real
> wait we have left for the gpu is the one under i915_sw_fence. I think
> we could simply switch i915_mutex_lock_interruptible calls in atomic
> modeset over mutex_lock_interruptible? Or is there another can of
> worms I'm missing?

Obviously, because that's what we're doing already. But I don't have
the DRM_ERROR from i915_gem_wait_for_error anywhere in my logs either,
so not clear what exactly is going on ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch