Re: [PATCH 3/3] drm/i915: Markup expected timeline locks for i915_active

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> As every i915_active_request should be serialised by a dedicated lock,
> i915_active consists of a tree of locks; one for each node. Markup up
> the i915_active_request with what lock is supposed to be guarding it so
> that we can verify that the serialised updated are indeed serialised.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/display/intel_overlay.c  |  2 +-
>  .../gpu/drm/i915/gem/i915_gem_client_blt.c    |  2 +-
>  drivers/gpu/drm/i915/gem/i915_gem_context.c   |  2 +-
>  drivers/gpu/drm/i915/gt/intel_context.c       | 11 +++--------
>  drivers/gpu/drm/i915/gt/intel_engine_pool.h   |  2 +-
>  drivers/gpu/drm/i915/gt/intel_timeline.c      |  7 +++----
>  drivers/gpu/drm/i915/gt/selftest_timeline.c   |  4 ++++
>  .../gpu/drm/i915/gt/selftests/mock_timeline.c |  2 +-
>  drivers/gpu/drm/i915/i915_active.c            | 19 +++++++++++++++----
>  drivers/gpu/drm/i915/i915_active.h            | 12 ++++++++++--
>  drivers/gpu/drm/i915/i915_active_types.h      |  3 +++
>  drivers/gpu/drm/i915/i915_vma.c               |  4 ++--
>  drivers/gpu/drm/i915/selftests/i915_active.c  |  3 +--
>  13 files changed, 46 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_overlay.c b/drivers/gpu/drm/i915/display/intel_overlay.c
> index e1248eace0e1..eca41c4a5aa6 100644
> --- a/drivers/gpu/drm/i915/display/intel_overlay.c
> +++ b/drivers/gpu/drm/i915/display/intel_overlay.c
> @@ -230,7 +230,7 @@ alloc_request(struct intel_overlay *overlay, void (*fn)(struct intel_overlay *))
>  	if (IS_ERR(rq))
>  		return rq;
>  
> -	err = i915_active_ref(&overlay->last_flip, rq->fence.context, rq);
> +	err = i915_active_ref(&overlay->last_flip, rq->timeline, rq);
>  	if (err) {
>  		i915_request_add(rq);
>  		return ERR_PTR(err);
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_client_blt.c b/drivers/gpu/drm/i915/gem/i915_gem_client_blt.c
> index 6a4e84157bf2..818ac6915bc5 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_client_blt.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_client_blt.c
> @@ -211,7 +211,7 @@ static void clear_pages_worker(struct work_struct *work)
>  	 * keep track of the GPU activity within this vma/request, and
>  	 * propagate the signal from the request to w->dma.
>  	 */
> -	err = i915_active_ref(&vma->active, rq->fence.context, rq);
> +	err = i915_active_ref(&vma->active, rq->timeline, rq);
>  	if (err)
>  		goto out_request;
>  
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index a6b0cb714292..cd1fd2e5423a 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -908,7 +908,7 @@ static int context_barrier_task(struct i915_gem_context *ctx,
>  		if (emit)
>  			err = emit(rq, data);
>  		if (err == 0)
> -			err = i915_active_ref(&cb->base, rq->fence.context, rq);
> +			err = i915_active_ref(&cb->base, rq->timeline, rq);
>  
>  		i915_request_add(rq);
>  		if (err)
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> index 9114953bf920..f55691d151ae 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.c
> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> @@ -306,10 +306,10 @@ int intel_context_prepare_remote_request(struct intel_context *ce,
>  
>  		/* Queue this switch after current activity by this context. */
>  		err = i915_active_request_set(&tl->last_request, rq);
> +		mutex_unlock(&tl->mutex);
>  		if (err)
> -			goto unlock;
> +			return err;
>  	}
> -	lockdep_assert_held(&tl->mutex);
>  
>  	/*
>  	 * Guarantee context image and the timeline remains pinned until the
> @@ -319,12 +319,7 @@ int intel_context_prepare_remote_request(struct intel_context *ce,
>  	 * words transfer the pinned ce object to tracked active request.
>  	 */
>  	GEM_BUG_ON(i915_active_is_idle(&ce->active));
> -	err = i915_active_ref(&ce->active, rq->fence.context, rq);
> -
> -unlock:
> -	if (rq->timeline != tl)
> -		mutex_unlock(&tl->mutex);
> -	return err;
> +	return i915_active_ref(&ce->active, rq->timeline, rq);

There seem to have been so much work here for no apparent gains.
Good riddance.

>  }
>  
>  struct i915_request *intel_context_create_request(struct intel_context *ce)
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pool.h b/drivers/gpu/drm/i915/gt/intel_engine_pool.h
> index f7a0a660c1c9..8d069efd9457 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_pool.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_pool.h
> @@ -18,7 +18,7 @@ static inline int
>  intel_engine_pool_mark_active(struct intel_engine_pool_node *node,
>  			      struct i915_request *rq)
>  {
> -	return i915_active_ref(&node->active, rq->fence.context, rq);
> +	return i915_active_ref(&node->active, rq->timeline, rq);
>  }
>  
>  static inline void
> diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c
> index eafd94d5e211..02fbe11b671b 100644
> --- a/drivers/gpu/drm/i915/gt/intel_timeline.c
> +++ b/drivers/gpu/drm/i915/gt/intel_timeline.c
> @@ -254,7 +254,7 @@ int intel_timeline_init(struct intel_timeline *timeline,
>  
>  	mutex_init(&timeline->mutex);
>  
> -	INIT_ACTIVE_REQUEST(&timeline->last_request);
> +	INIT_ACTIVE_REQUEST(&timeline->last_request, &timeline->mutex);
>  	INIT_LIST_HEAD(&timeline->requests);
>  
>  	i915_syncmap_init(&timeline->sync);
> @@ -440,8 +440,7 @@ __intel_timeline_get_seqno(struct intel_timeline *tl,
>  	 * free it after the current request is retired, which ensures that
>  	 * all writes into the cacheline from previous requests are complete.
>  	 */
> -	err = i915_active_ref(&tl->hwsp_cacheline->active,
> -			      tl->fence_context, rq);
> +	err = i915_active_ref(&tl->hwsp_cacheline->active, tl, rq);
>  	if (err)
>  		goto err_cacheline;
>  
> @@ -492,7 +491,7 @@ int intel_timeline_get_seqno(struct intel_timeline *tl,
>  static int cacheline_ref(struct intel_timeline_cacheline *cl,
>  			 struct i915_request *rq)
>  {
> -	return i915_active_ref(&cl->active, rq->fence.context, rq);
> +	return i915_active_ref(&cl->active, rq->timeline, rq);
>  }
>  
>  int intel_timeline_read_hwsp(struct i915_request *from,
> diff --git a/drivers/gpu/drm/i915/gt/selftest_timeline.c b/drivers/gpu/drm/i915/gt/selftest_timeline.c
> index d54113697745..321481403165 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_timeline.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_timeline.c
> @@ -689,7 +689,9 @@ static int live_hwsp_wrap(void *arg)
>  
>  		tl->seqno = -4u;
>  
> +		mutex_lock_nested(&tl->mutex, SINGLE_DEPTH_NESTING);
>  		err = intel_timeline_get_seqno(tl, rq, &seqno[0]);
> +		mutex_unlock(&tl->mutex);
>  		if (err) {
>  			i915_request_add(rq);
>  			goto out;
> @@ -704,7 +706,9 @@ static int live_hwsp_wrap(void *arg)
>  		}
>  		hwsp_seqno[0] = tl->hwsp_seqno;
>  
> +		mutex_lock_nested(&tl->mutex, SINGLE_DEPTH_NESTING);
>  		err = intel_timeline_get_seqno(tl, rq, &seqno[1]);
> +		mutex_unlock(&tl->mutex);
>  		if (err) {
>  			i915_request_add(rq);
>  			goto out;
> diff --git a/drivers/gpu/drm/i915/gt/selftests/mock_timeline.c b/drivers/gpu/drm/i915/gt/selftests/mock_timeline.c
> index 5c549205828a..598170efcaf6 100644
> --- a/drivers/gpu/drm/i915/gt/selftests/mock_timeline.c
> +++ b/drivers/gpu/drm/i915/gt/selftests/mock_timeline.c
> @@ -15,7 +15,7 @@ void mock_timeline_init(struct intel_timeline *timeline, u64 context)
>  
>  	mutex_init(&timeline->mutex);
>  
> -	INIT_ACTIVE_REQUEST(&timeline->last_request);
> +	INIT_ACTIVE_REQUEST(&timeline->last_request, &timeline->mutex);
>  	INIT_LIST_HEAD(&timeline->requests);
>  
>  	i915_syncmap_init(&timeline->sync);
> diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
> index 2439c4f62ad8..df6164591702 100644
> --- a/drivers/gpu/drm/i915/i915_active.c
> +++ b/drivers/gpu/drm/i915/i915_active.c
> @@ -169,10 +169,11 @@ node_retire(struct i915_active_request *base, struct i915_request *rq)
>  }
>  
>  static struct i915_active_request *
> -active_instance(struct i915_active *ref, u64 idx)
> +active_instance(struct i915_active *ref, struct intel_timeline *tl)
>  {
>  	struct active_node *node, *prealloc;
>  	struct rb_node **p, *parent;
> +	u64 idx = tl->fence_context;
>  
>  	/*
>  	 * We track the most recently used timeline to skip a rbtree search
> @@ -211,7 +212,7 @@ active_instance(struct i915_active *ref, u64 idx)
>  	}
>  
>  	node = prealloc;
> -	i915_active_request_init(&node->base, NULL, node_retire);
> +	i915_active_request_init(&node->base, &tl->mutex, NULL, node_retire);
>  	node->ref = ref;
>  	node->timeline = idx;
>  
> @@ -294,18 +295,20 @@ __active_del_barrier(struct i915_active *ref, struct active_node *node)
>  }
>  
>  int i915_active_ref(struct i915_active *ref,
> -		    u64 timeline,
> +		    struct intel_timeline *tl,
>  		    struct i915_request *rq)
>  {
>  	struct i915_active_request *active;
>  	int err;
>  
> +	lockdep_assert_held(&tl->mutex);
> +
>  	/* Prevent reaping in case we malloc/wait while building the tree */
>  	err = i915_active_acquire(ref);
>  	if (err)
>  		return err;
>  
> -	active = active_instance(ref, timeline);
> +	active = active_instance(ref, tl);
>  	if (!active) {
>  		err = -ENOMEM;
>  		goto out;
> @@ -596,6 +599,10 @@ int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
>  				goto unwind;
>  			}
>  
> +#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
> +			node->base.lock =
> +				&engine->kernel_context->timeline->mutex;
> +#endif
>  			RCU_INIT_POINTER(node->base.request, NULL);
>  			node->base.retire = node_retire;
>  			node->timeline = idx;
> @@ -701,6 +708,10 @@ int i915_active_request_set(struct i915_active_request *active,
>  {
>  	int err;
>  
> +#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
> +	lockdep_assert_held(active->lock);
> +#endif
> +
>  	/* Must maintain ordering wrt previous active requests */
>  	err = i915_request_await_active_request(rq, active);
>  	if (err)
> diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
> index f6d730cf2fe6..f95058f99057 100644
> --- a/drivers/gpu/drm/i915/i915_active.h
> +++ b/drivers/gpu/drm/i915/i915_active.h
> @@ -58,15 +58,20 @@ void i915_active_retire_noop(struct i915_active_request *active,
>   */
>  static inline void
>  i915_active_request_init(struct i915_active_request *active,
> +			 struct mutex *lock,
>  			 struct i915_request *rq,
>  			 i915_active_retire_fn retire)
>  {
>  	RCU_INIT_POINTER(active->request, rq);
>  	INIT_LIST_HEAD(&active->link);
>  	active->retire = retire ?: i915_active_retire_noop;
> +#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
> +	active->lock = lock;
> +#endif
>  }
>  
> -#define INIT_ACTIVE_REQUEST(name) i915_active_request_init((name), NULL, NULL)
> +#define INIT_ACTIVE_REQUEST(name, lock) \
> +	i915_active_request_init((name), (lock), NULL, NULL)
>  
>  /**
>   * i915_active_request_set - updates the tracker to watch the current request
> @@ -81,6 +86,9 @@ static inline void
>  __i915_active_request_set(struct i915_active_request *active,
>  			  struct i915_request *request)
>  {
> +#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
> +	lockdep_assert_held(active->lock);
> +#endif
>  	list_move(&active->link, &request->active_list);
>  	rcu_assign_pointer(active->request, request);
>  }
> @@ -362,7 +370,7 @@ void __i915_active_init(struct drm_i915_private *i915,
>  } while (0)
>  
>  int i915_active_ref(struct i915_active *ref,
> -		    u64 timeline,
> +		    struct intel_timeline *tl,
>  		    struct i915_request *rq);
>  
>  int i915_active_wait(struct i915_active *ref);
> diff --git a/drivers/gpu/drm/i915/i915_active_types.h b/drivers/gpu/drm/i915/i915_active_types.h
> index ae3ee441c114..d857bd12aa7e 100644
> --- a/drivers/gpu/drm/i915/i915_active_types.h
> +++ b/drivers/gpu/drm/i915/i915_active_types.h
> @@ -24,6 +24,9 @@ struct i915_active_request {
>  	struct i915_request __rcu *request;
>  	struct list_head link;
>  	i915_active_retire_fn retire;
> +#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
> +	struct mutex *lock;

Checkpatch thinks the usage should be somehow stated with comment.

So put something like
/* Incorporeal. Ref piggypacking timeline for lockdep */

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> +#endif
>  };
>  
>  struct active_node;
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index a32243951b29..73b02234affe 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -903,14 +903,14 @@ int i915_vma_move_to_active(struct i915_vma *vma,
>  	 * add the active reference first and queue for it to be dropped
>  	 * *last*.
>  	 */
> -	err = i915_active_ref(&vma->active, rq->fence.context, rq);
> +	err = i915_active_ref(&vma->active, rq->timeline, rq);
>  	if (unlikely(err))
>  		return err;
>  
>  	if (flags & EXEC_OBJECT_WRITE) {
>  		if (intel_frontbuffer_invalidate(obj->frontbuffer, ORIGIN_CS))
>  			i915_active_ref(&obj->frontbuffer->write,
> -					rq->fence.context,
> +					rq->timeline,
>  					rq);
>  
>  		dma_resv_add_excl_fence(vma->resv, &rq->fence);
> diff --git a/drivers/gpu/drm/i915/selftests/i915_active.c b/drivers/gpu/drm/i915/selftests/i915_active.c
> index e5cd5d47e380..77d844ac8b71 100644
> --- a/drivers/gpu/drm/i915/selftests/i915_active.c
> +++ b/drivers/gpu/drm/i915/selftests/i915_active.c
> @@ -110,8 +110,7 @@ __live_active_setup(struct drm_i915_private *i915)
>  						       submit,
>  						       GFP_KERNEL);
>  		if (err >= 0)
> -			err = i915_active_ref(&active->base,
> -					      rq->fence.context, rq);
> +			err = i915_active_ref(&active->base, rq->timeline, rq);
>  		i915_request_add(rq);
>  		if (err) {
>  			pr_err("Failed to track active ref!\n");
> -- 
> 2.23.0.rc1
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