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

[John Harrison <John.C.Harrison@xxxxxxxxx>]

On 05/03/2015 15:27, Tomas Elf wrote:
> On 19/02/2015 17:17, John.C.Harrison@xxxxxxxxx wrote:
> > From: John Harrison <John.C.Harrison@xxxxxxxxx>
> >
> > 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@xxxxxxxxx>
> > ---
> >   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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