Re: [Intel-gfx] [PATCH 1/6] drm/i915: Hold reference to previous active fence as we queue

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

On 03/02/2020 09:41, Chris Wilson wrote:
> Take a reference to the previous exclusive fence on the i915_active, as
> we wish to add an await to it in the caller (and so must prevent it from
> being freed until we have completed that task).
> 
> Fixes: e3793468b466 ("drm/i915: Use the async worker to avoid reclaim tainting the ggtt->mutex")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Matthew Auld <matthew.auld@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_active.c | 6 +++++-
>   drivers/gpu/drm/i915/i915_vma.c    | 4 +++-
>   2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
> index da58e5d084f4..9ccb931a733e 100644
> --- a/drivers/gpu/drm/i915/i915_active.c
> +++ b/drivers/gpu/drm/i915/i915_active.c
> @@ -398,9 +398,13 @@ i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f)
>   	/* We expect the caller to manage the exclusive timeline ordering */
>   	GEM_BUG_ON(i915_active_is_idle(ref));
>   
> +	rcu_read_lock();
>   	prev = __i915_active_fence_set(&ref->excl, f);
> -	if (!prev)
> +	if (prev)
> +		prev = dma_fence_get_rcu(prev);
> +	else
>   		atomic_inc(&ref->count);
> +	rcu_read_unlock();
>   
>   	return prev;
>   }
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index e801e28de470..74dc3ba59ce5 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -422,10 +422,12 @@ int i915_vma_bind(struct i915_vma *vma,
>   		 * execution and not content or object's backing store lifetime.
>   		 */
>   		prev = i915_active_set_exclusive(&vma->active, &work->base.dma);
> -		if (prev)
> +		if (prev) {
>   			__i915_sw_fence_await_dma_fence(&work->base.chain,
>   							prev,
>   							&work->cb);
> +			dma_fence_put(prev);
> +		}
>   
>   		work->base.dma.error = 0; /* enable the queue_work() */
>   
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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