Re: [PATCH 08/53] drm/i915: Update alloc_request to return the allocated request

[Tomas Elf <tomas.elf@intel.com>]

On 19/02/2015 17:17, John.C.Harrison@Intel.com wrote:
> From: John Harrison <John.C.Harrison@Intel.com>
>
> The alloc_request() function does not actually return the newly allocated
> request. Instead, it must be pulled from ring->outstanding_lazy_request. This
> patch fixes this so that code can create a request and start using it knowing
> exactly which request it actually owns.
>
> For: VIZ-5115
> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
> ---
>   drivers/gpu/drm/i915/i915_drv.h            |    3 ++-
>   drivers/gpu/drm/i915/i915_gem_execbuffer.c |    3 ++-
>   drivers/gpu/drm/i915/intel_lrc.c           |   13 +++++++++----
>   drivers/gpu/drm/i915/intel_lrc.h           |    3 ++-
>   drivers/gpu/drm/i915/intel_ringbuffer.c    |   14 ++++++++++----
>   drivers/gpu/drm/i915/intel_ringbuffer.h    |    3 ++-
>   6 files changed, 27 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 87a4a2e..90223f208 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1909,7 +1909,8 @@ struct drm_i915_private {
>   	/* Abstract the submission mechanism (legacy ringbuffer or execlists) away */
>   	struct {
>   		int (*alloc_request)(struct intel_engine_cs *ring,
> -				     struct intel_context *ctx);
> +				     struct intel_context *ctx,
> +				     struct drm_i915_gem_request **req_out);
>   		int (*do_execbuf)(struct i915_execbuffer_params *params,
>   				  struct drm_i915_gem_execbuffer2 *args,
>   				  struct list_head *vmas);
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index 61471e9..37dcc6f 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -1353,6 +1353,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
>   	struct i915_address_space *vm;
>   	struct i915_execbuffer_params params_master; /* XXX: will be removed later */
>   	struct i915_execbuffer_params *params = &params_master;
> +	struct drm_i915_gem_request *request;

Please initialize request to NULL. If you accidentally dereference it 
before it is allocated (seeing as the allocation is several pages down 
from here) you get a null pointer exception, which is a clear indication 
that you did something stupid. Otherwise it's not clear what will happen 
(sure, page fault, but null pointer exception is a better failure 
indication).

Thanks,
Tomas

>   	const u32 ctx_id = i915_execbuffer2_get_context_id(*args);
>   	u32 dispatch_flags;
>   	int ret;
> @@ -1531,7 +1532,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
>   		params->batch_obj_vm_offset = i915_gem_obj_offset(batch_obj, vm);
>
>   	/* Allocate a request for this batch buffer nice and early. */
> -	ret = dev_priv->gt.alloc_request(ring, ctx);
> +	ret = dev_priv->gt.alloc_request(ring, ctx, &request);
>   	if (ret)
>   		goto err;
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 8628abf..c3c783f 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -857,13 +857,17 @@ void intel_lr_context_unpin(struct intel_engine_cs *ring,
>   }
>
>   int intel_logical_ring_alloc_request(struct intel_engine_cs *ring,
> -				     struct intel_context *ctx)
> +				     struct intel_context *ctx,
> +				     struct drm_i915_gem_request **req_out)
>   {
>   	struct drm_i915_gem_request *request;
>   	struct drm_i915_private *dev_private = ring->dev->dev_private;
>   	int ret;
>
> -	if (ring->outstanding_lazy_request)
> +	if (!req_out)
> +		return -EINVAL;
> +
> +	if ((*req_out = ring->outstanding_lazy_request) != NULL)
>   		return 0;
>
>   	request = kzalloc(sizeof(*request), GFP_KERNEL);
> @@ -898,7 +902,7 @@ int intel_logical_ring_alloc_request(struct intel_engine_cs *ring,
>   	i915_gem_context_reference(request->ctx);
>   	request->ringbuf = ctx->engine[ring->id].ringbuf;
>
> -	ring->outstanding_lazy_request = request;
> +	*req_out = ring->outstanding_lazy_request = request;
>   	return 0;
>   }
>
> @@ -1051,6 +1055,7 @@ static int logical_ring_prepare(struct intel_ringbuffer *ringbuf,
>   int intel_logical_ring_begin(struct intel_ringbuffer *ringbuf,
>   			     struct intel_context *ctx, int num_dwords)
>   {
> +	struct drm_i915_gem_request *req;
>   	struct intel_engine_cs *ring = ringbuf->ring;
>   	struct drm_device *dev = ring->dev;
>   	struct drm_i915_private *dev_priv = dev->dev_private;
> @@ -1066,7 +1071,7 @@ int intel_logical_ring_begin(struct intel_ringbuffer *ringbuf,
>   		return ret;
>
>   	/* Preallocate the olr before touching the ring */
> -	ret = intel_logical_ring_alloc_request(ring, ctx);
> +	ret = intel_logical_ring_alloc_request(ring, ctx, &req);
>   	if (ret)
>   		return ret;
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.h b/drivers/gpu/drm/i915/intel_lrc.h
> index 3cc38bd..77de8ac 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.h
> +++ b/drivers/gpu/drm/i915/intel_lrc.h
> @@ -37,7 +37,8 @@
>
>   /* Logical Rings */
>   int __must_check intel_logical_ring_alloc_request(struct intel_engine_cs *ring,
> -						  struct intel_context *ctx);
> +						  struct intel_context *ctx,
> +						  struct drm_i915_gem_request **req_out);
>   void intel_logical_ring_stop(struct intel_engine_cs *ring);
>   void intel_logical_ring_cleanup(struct intel_engine_cs *ring);
>   int intel_logical_rings_init(struct drm_device *dev);
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 635707a..1a9f884 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -2164,13 +2164,18 @@ int intel_ring_idle(struct intel_engine_cs *ring)
>   }
>
>   int
> -intel_ring_alloc_request(struct intel_engine_cs *ring, struct intel_context *ctx)
> +intel_ring_alloc_request(struct intel_engine_cs *ring,
> +			 struct intel_context *ctx,
> +			 struct drm_i915_gem_request **req_out)
>   {
>   	int ret;
>   	struct drm_i915_gem_request *request;
>   	struct drm_i915_private *dev_private = ring->dev->dev_private;
>
> -	if (ring->outstanding_lazy_request)
> +	if (!req_out)
> +		return -EINVAL;
> +
> +	if ((*req_out = ring->outstanding_lazy_request) != NULL)
>   		return 0;
>
>   	request = kzalloc(sizeof(*request), GFP_KERNEL);
> @@ -2188,7 +2193,7 @@ intel_ring_alloc_request(struct intel_engine_cs *ring, struct intel_context *ctx
>   		return ret;
>   	}
>
> -	ring->outstanding_lazy_request = request;
> +	*req_out = ring->outstanding_lazy_request = request;
>   	return 0;
>   }
>
> @@ -2216,6 +2221,7 @@ static int __intel_ring_prepare(struct intel_engine_cs *ring,
>   int intel_ring_begin(struct intel_engine_cs *ring,
>   		     int num_dwords)
>   {
> +	struct drm_i915_gem_request *req;
>   	struct drm_i915_private *dev_priv = ring->dev->dev_private;
>   	int ret;
>
> @@ -2229,7 +2235,7 @@ int intel_ring_begin(struct intel_engine_cs *ring,
>   		return ret;
>
>   	/* Preallocate the olr before touching the ring */
> -	ret = intel_ring_alloc_request(ring, NULL);
> +	ret = intel_ring_alloc_request(ring, NULL, &req);
>   	if (ret)
>   		return ret;
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 2fd960a..4f8a14a 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -393,7 +393,8 @@ void intel_cleanup_ring_buffer(struct intel_engine_cs *ring);
>   int __must_check intel_ring_begin(struct intel_engine_cs *ring, int n);
>   int __must_check intel_ring_cacheline_align(struct intel_engine_cs *ring);
>   int __must_check intel_ring_alloc_request(struct intel_engine_cs *ring,
> -					  struct intel_context *ctx);
> +					  struct intel_context *ctx,
> +					  struct drm_i915_gem_request **req_out);
>   static inline void intel_ring_emit(struct intel_engine_cs *ring,
>   				   u32 data)
>   {
>

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx