Re: [PATCH v1] drm/i915: Fix a false alert of memory leak when free LRC

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Nov 19, 2015 at 04:10:26PM -0800, yu.dai@intel.com wrote:
> From: Alex Dai <yu.dai@intel.com>
> 
> There is a memory leak warning message from i915_gem_context_clean
> when GuC submission is enabled. The reason is that when LRC is
> released, its ppgtt could be still referenced. The assumption that
> all VMAs are unbound during release of LRC is not true.
> 
> v1: Move the code inside i915_gem_context_clean() to where ppgtt is
> released because it is not cleaning context anyway but ppgtt.
> 
> Signed-off-by: Alex Dai <yu.dai@intel.com>

retire__read drops the ctx (and hence ppgtt) reference too early,
resulting in us hitting the WARNING. See the giant thread with Tvrtko,
Chris and me:

http://www.spinics.net/lists/intel-gfx/msg78918.html

Would be great if someone could test the diff I posted in there.
-Daniel

> ---
>  drivers/gpu/drm/i915/i915_gem_context.c | 24 ------------------------
>  drivers/gpu/drm/i915/i915_gem_gtt.c     | 12 ++++++++++++
>  2 files changed, 12 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index 204dc7c..cc5c8e6 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -133,23 +133,6 @@ static int get_context_size(struct drm_device *dev)
>  	return ret;
>  }
>  
> -static void i915_gem_context_clean(struct intel_context *ctx)
> -{
> -	struct i915_hw_ppgtt *ppgtt = ctx->ppgtt;
> -	struct i915_vma *vma, *next;
> -
> -	if (!ppgtt)
> -		return;
> -
> -	WARN_ON(!list_empty(&ppgtt->base.active_list));
> -
> -	list_for_each_entry_safe(vma, next, &ppgtt->base.inactive_list,
> -				 mm_list) {
> -		if (WARN_ON(__i915_vma_unbind_no_wait(vma)))
> -			break;
> -	}
> -}
> -
>  void i915_gem_context_free(struct kref *ctx_ref)
>  {
>  	struct intel_context *ctx = container_of(ctx_ref, typeof(*ctx), ref);
> @@ -159,13 +142,6 @@ void i915_gem_context_free(struct kref *ctx_ref)
>  	if (i915.enable_execlists)
>  		intel_lr_context_free(ctx);
>  
> -	/*
> -	 * This context is going away and we need to remove all VMAs still
> -	 * around. This is to handle imported shared objects for which
> -	 * destructor did not run when their handles were closed.
> -	 */
> -	i915_gem_context_clean(ctx);
> -
>  	i915_ppgtt_put(ctx->ppgtt);
>  
>  	if (ctx->legacy_hw_ctx.rcs_state)
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 016739e..d36943c 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -2214,6 +2214,7 @@ void  i915_ppgtt_release(struct kref *kref)
>  {
>  	struct i915_hw_ppgtt *ppgtt =
>  		container_of(kref, struct i915_hw_ppgtt, ref);
> +	struct i915_vma *vma, *next;
>  
>  	trace_i915_ppgtt_release(&ppgtt->base);
>  
> @@ -2221,6 +2222,17 @@ void  i915_ppgtt_release(struct kref *kref)
>  	WARN_ON(!list_empty(&ppgtt->base.active_list));
>  	WARN_ON(!list_empty(&ppgtt->base.inactive_list));
>  
> +	/*
> +	 * This ppgtt is going away and we need to remove all VMAs still
> +	 * around. This is to handle imported shared objects for which
> +	 * destructor did not run when their handles were closed.
> +	 */
> +	list_for_each_entry_safe(vma, next, &ppgtt->base.inactive_list,
> +				 mm_list) {
> +		if (WARN_ON(__i915_vma_unbind_no_wait(vma)))
> +			break;
> +	}
> +
>  	list_del(&ppgtt->base.global_link);
>  	drm_mm_takedown(&ppgtt->base.mm);
>  
> -- 
> 2.5.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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