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

Tomas Elf
2015-03-05T15:27:21Z

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)
> {
>