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

Tomas Elf
2015-03-05T20:13:09Z

On 05/03/2015 15:46, John Harrison wrote:
> On 05/03/2015 15:27, Tomas Elf wrote:
>> 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).
>
> That should generate a 'use before assignment' compiler warning.

That assumes that the developer in question isn't too busy hacking to
check for warnings (in all honesty that developer probably would've been
me ;)). Sure, you should always check for warnings but if we can save
this developer some time by giving them a clear run-time indication
aside from the compile-time warning then that would not be a bad thing.
I've been there myself a few times and I know times in the past where
this would've saved me the time it takes to rebuild and redeploy the
kernel once.

Thanks,
Tomas

>
>>
>> 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)
>>> {
>>>
>>
>