Re: [PATCH 13/17] drm/radeon: Remove custom dma_fence_ops->wait implementation

["Christian König" <ckoenig.leichtzumerken-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Am 30.04.2018 um 17:38 schrieb Daniel Vetter:
> On Sun, Apr 29, 2018 at 09:08:31AM +0200, Christian König wrote:
>> NAK, there is a subtitle but major difference:
>>
>>> -		if (rdev->needs_reset) {
>>> -			t = -EDEADLK;
>>> -			break;
>>> -		}
>> Without that the whole radeon GPU reset code breaks.
> Oops I've missed that. How does this work when you register a callback
> using ->enable_signaling and then block on it? Everything just dies?

The short answer is we simply avoid using enable_signaling() from inside 
driver IOCTLs.

> We have lots of users of that for buffer/fence sharing. A really ugly, but
> probably working fix for this would be a kthread worker that just looks
> for ->needs_reset and force-completes all fences with
> dma_fence_set_error(-EIO), which is kinda what's supposed to happen here
> anyway.

That actually won't help. Radeon does this dance to return an error from 
dma_fence_wait() when the GPU needs a reset.

This way all IOCTLs should return to userspace with -EAGAIN and when 
they are restarted we block for the running GPU reset to finish.

I was against this approach, but it works as long as radeon only has to 
deal with it's own fences.

Christian.

> -Daniel
>
>> Regards,
>> Christian.
>>
>>
>> Am 27.04.2018 um 08:17 schrieb Daniel Vetter:
>>> It's a copy of dma_fence_default_wait, written slightly differently.
>>>
>>> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>>> Cc: Alex Deucher <alexander.deucher@amd.com>
>>> Cc: "Christian König" <christian.koenig@amd.com>
>>> Cc: "David (ChunMing) Zhou" <David1.Zhou@amd.com>
>>> Cc: amd-gfx@lists.freedesktop.org
>>> ---
>>>    drivers/gpu/drm/radeon/radeon_fence.c | 63 ---------------------------
>>>    1 file changed, 63 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/radeon/radeon_fence.c b/drivers/gpu/drm/radeon/radeon_fence.c
>>> index e86f2bd38410..32690a525bfc 100644
>>> --- a/drivers/gpu/drm/radeon/radeon_fence.c
>>> +++ b/drivers/gpu/drm/radeon/radeon_fence.c
>>> @@ -1051,72 +1051,9 @@ static const char *radeon_fence_get_timeline_name(struct dma_fence *f)
>>>    	}
>>>    }
>>> -static inline bool radeon_test_signaled(struct radeon_fence *fence)
>>> -{
>>> -	return test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->base.flags);
>>> -}
>>> -
>>> -struct radeon_wait_cb {
>>> -	struct dma_fence_cb base;
>>> -	struct task_struct *task;
>>> -};
>>> -
>>> -static void
>>> -radeon_fence_wait_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
>>> -{
>>> -	struct radeon_wait_cb *wait =
>>> -		container_of(cb, struct radeon_wait_cb, base);
>>> -
>>> -	wake_up_process(wait->task);
>>> -}
>>> -
>>> -static signed long radeon_fence_default_wait(struct dma_fence *f, bool intr,
>>> -					     signed long t)
>>> -{
>>> -	struct radeon_fence *fence = to_radeon_fence(f);
>>> -	struct radeon_device *rdev = fence->rdev;
>>> -	struct radeon_wait_cb cb;
>>> -
>>> -	cb.task = current;
>>> -
>>> -	if (dma_fence_add_callback(f, &cb.base, radeon_fence_wait_cb))
>>> -		return t;
>>> -
>>> -	while (t > 0) {
>>> -		if (intr)
>>> -			set_current_state(TASK_INTERRUPTIBLE);
>>> -		else
>>> -			set_current_state(TASK_UNINTERRUPTIBLE);
>>> -
>>> -		/*
>>> -		 * radeon_test_signaled must be called after
>>> -		 * set_current_state to prevent a race with wake_up_process
>>> -		 */
>>> -		if (radeon_test_signaled(fence))
>>> -			break;
>>> -
>>> -		if (rdev->needs_reset) {
>>> -			t = -EDEADLK;
>>> -			break;
>>> -		}
>>> -
>>> -		t = schedule_timeout(t);
>>> -
>>> -		if (t > 0 && intr && signal_pending(current))
>>> -			t = -ERESTARTSYS;
>>> -	}
>>> -
>>> -	__set_current_state(TASK_RUNNING);
>>> -	dma_fence_remove_callback(f, &cb.base);
>>> -
>>> -	return t;
>>> -}
>>> -
>>>    const struct dma_fence_ops radeon_fence_ops = {
>>>    	.get_driver_name = radeon_fence_get_driver_name,
>>>    	.get_timeline_name = radeon_fence_get_timeline_name,
>>>    	.enable_signaling = radeon_fence_enable_signaling,
>>>    	.signaled = radeon_fence_is_signaled,
>>> -	.wait = radeon_fence_default_wait,
>>> -	.release = NULL,
>>>    };

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