linux-kernel - Re: [PATCH v8 5/8] arm64: Use of_cpu_node_to

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Date:   Tue, 17 Oct 2017 17:42:57 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        robh@...nel.org, sudeep.holla@....com, frowand.list@...il.com,
        devicetree@...r.kernel.org, Jonathan.Cameron@...wei.com,
        marc.zyngier@....com, peterz@...radead.org,
        mathieu.poirier@...aro.org, leo.yan@...aro.org,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v8 5/8] arm64: Use of_cpu_node_to_id helper for CPU
 topology parsing

On 17/10/17 17:20, Suzuki K Poulose wrote:
> On 17/10/17 17:11, Will Deacon wrote:
>> On Tue, Oct 17, 2017 at 04:24:23PM +0100, Mark Rutland wrote:
>>> On Tue, Oct 10, 2017 at 11:33:00AM +0100, Suzuki K Poulose wrote:
>>>> Make use of the new generic helper to convert an of_node of a CPU
>>>> to the logical CPU id in parsing the topology.
>>>>
>>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>>> Cc: Leo Yan <leo.yan@...aro.org>
>>>> Cc: Will Deacon <will.deacon@....com>
>>>> Cc: Mark Rutland <mark.rutland@....com>
>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>>>
>>> This looks sane to me, but it will need an ack from Will or Catalin.
>>>
>>> FWIW:
>>>
>>> Acked-by: Mark Rutland <mark.rutland@....com>
>>>
>>> Thanks,
>>> Mark.
>>>
>>>> ---
>>>>   arch/arm64/kernel/topology.c | 16 ++++++----------
>>>>   1 file changed, 6 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
>>>> index 8d48b233e6ce..21868530018e 100644
>>>> --- a/arch/arm64/kernel/topology.c
>>>> +++ b/arch/arm64/kernel/topology.c
>>>> @@ -37,18 +37,14 @@ static int __init get_cpu_for_node(struct device_node *node)
>>>>       if (!cpu_node)
>>>>           return -1;
>>>> -    for_each_possible_cpu(cpu) {
>>>> -        if (of_get_cpu_node(cpu, NULL) == cpu_node) {
>>>> -            topology_parse_cpu_capacity(cpu_node, cpu);
>>>> -            of_node_put(cpu_node);
>>>> -            return cpu;
>>>> -        }
>>>> -    }
>>>> -
>>>> -    pr_crit("Unable to find CPU node for %pOF\n", cpu_node);
>>>> +    cpu = of_cpu_node_to_id(cpu_node);
>>>> +    if (cpu >= 0)
>>>> +        topology_parse_cpu_capacity(cpu_node, cpu);
>>>> +    else
>>>> +        pr_crit("Unable to find CPU node for %pOF\n", cpu_node);
>>>>       of_node_put(cpu_node);
>>
>> This of_node_put is confusing me. Since of_cpu_node_to_id appears to be
>> balanced with its use of the node refcount, is this one intended to pair
>> with the earlier call to of_parse_phandle?
> 
> Yes.
> 
>   If so, does that mainline is
>> currently broken here because it doesn't drop the refcount twice for the
>> matching node?
> 
> No. This of_node_put is for the failure case where we couldn't match a CPU.
> In the success case, it is dropped just before we return the result within
> the loop.

As we discussed offline, there is indeed a missing of_node_put() for all the
nodes we loop through to match. But with this change, we have fixed that.
And I don't think it is worth sending to stable.

Cheers
Suzuki