[Intel-gfx] [RFC v2 02/12] drm/i915/svm: Runtime (RT) allocator support

[Jason Gunthorpe]

On Fri, Dec 13, 2019 at 01:56:04PM -0800, Niranjana Vishwanathapura wrote:
  
> +	ctx = i915_gem_context_lookup(file->driver_priv, args->rsvd1);
> +	if (!ctx || !rcu_access_pointer(ctx->vm))
> +		return -ENOENT;
> +
> +	rcu_read_lock();
> +	vm = i915_vm_get(ctx->vm);
> +	rcu_read_unlock();

This looks like wrong use of RCU to me.

Getting a rcu lock and not calling rcu_dereference under it is
basically guarenteed to be wrong..

Jason