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

[John Harrison <John.C.Harrison@Intel.com>]

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.

>
> 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)
>>   {
>>
>

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