Messages in this thread | | | Date | Thu, 14 Apr 2016 11:10:54 +0100 | From | Mark Rutland <> | Subject | Re: [Question] refcount of DT node |
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On Thu, Apr 14, 2016 at 04:47:57PM +0900, Masahiro Yamada wrote: > Hi experts. > > My understanding of refcount of DT node is poor. > Please help me understand it correctly. > > Sorry if I am asking stupid questions. > > > [1] Does this reference count exist for Overlay? > Is a node freed when its refcount becomes zero?
I'm not familiar with the way that overlays are intended to work, but generally this is true, and I believe the same applies.
Pantelis, please correct me if I am wrong on that front.
> [2] When of_node_put() should be called, > or should not be called? > > > Shouldn't of_node_put() be called > when we are still referencing to any of its properties? > > For example, cpu_read_enable_method() > in arch/arm64/kernel/cpu_ops.c > returns a pointer to the property value > instead of creating a copy of it. > > In this case, of_node_put() should not be called > because we are still referencing the DT property > (in other words, referencing to the DT node indirectly). > > Am I right?
Yes, the node should not be freed while its data is referred to.
We are leaking a ref there, though, as we no longer refer to that data after cpu_read_ops().
Fixing that will require some restructuring. We don't expect a CPU node to need to disappear, so while it's currently not strictly correct the code shouldn't lead to any adverse behaviour.
> [3] Is the following code correct? > > np = of_find_compatible_node(NULL, NULL,"foo-node"); > of_node_put(np); > ret = of_address_to_resource(np, 0, &res); > if (ret) { > pr_err("failed to get resource\n"); > return ret; > } > > Actually I wrote the code above, and it was applied. > > But, the node is still referenced while of_address_to_resource() is being run. > > So the correct code should be as follows? > > np = of_find_compatible_node(NULL, NULL,"foo-node"); > ret = of_address_to_resource(np, 0, &res); > of_node_put(np); > if (ret) { > pr_err("failed to get resource\n"); > return ret; > }
It is correctly balanced, yes.
If you don't need to keep the node for future use, this is fine.
Mark.
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