linux-kernel - Re: [PATCH] of: resolver: Add missing of_node

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Date:	Wed, 27 Jan 2016 20:02:45 +0200
From:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Amitoj Kaur Chawla <amitoj1606@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Devicetree List <devicetree@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	julia.lawall@...6.fr
Subject: Re: [PATCH] of: resolver: Add missing of_node_put

Hi Mark,

> On Jan 27, 2016, at 18:21 , Mark Rutland <mark.rutland@....com> wrote:
> 
> On Wed, Jan 27, 2016 at 06:14:00PM +0200, Pantelis Antoniou wrote:
>> Hi Mark,
>> 
>>> On Jan 27, 2016, at 18:05 , Mark Rutland <mark.rutland@....com> wrote:
>>> 
>>> On Wed, Jan 27, 2016 at 08:50:17PM +0530, Amitoj Kaur Chawla wrote:
>>>> for_each_child_of_node performs an of_node_get on each iteration, so
>>>> to break out of the loop an of_node_put is required.
>>>> 
>>>> Found using Coccinelle. The semantic patch used for this is as follows:
>>>> 
>>>> // <smpl>
>>>> @@
>>>> expression e;
>>>> local idexpression n;
>>>> @@
>>>> 
>>>> for_each_child_of_node(..., n) {
>>>>  ... when != of_node_put(n)
>>>>      when != e = n
>>>> (
>>>>  return n;
>>>> |
>>>> +  of_node_put(n);
>>>> ?  return ...;
>>>> )
>>>>  ...
>>>> }
>>>> // </smpl
>>>> 
>>>> Signed-off-by: Amitoj Kaur Chawla <amitoj1606@...il.com>
>>>> ---
>>>> drivers/of/resolver.c | 4 +++-
>>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>> 
>>>> diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
>>>> index 640eb4c..e2a0143 100644
>>>> --- a/drivers/of/resolver.c
>>>> +++ b/drivers/of/resolver.c
>>>> @@ -40,8 +40,10 @@ static struct device_node *__of_find_node_by_full_name(struct device_node *node,
>>>> 
>>>> 	for_each_child_of_node(node, child) {
>>>> 		found = __of_find_node_by_full_name(child, full_name);
>>>> -		if (found != NULL)
>>>> +		if (found != NULL) {
>>>> +			of_node_put(child);
>>>> 			return found;
>>>> +		}
>>>> 	}
>>>> 
>>>> 	return NULL;
>>> 
>>> I don't think this is quite right. When child == found, this change will
>>> leave it decremented.
>>> 
>> 
>> 
>> This patch is bogus. 
>> 
>> __of_find_node_by_full_name() is not taking a reference on the node if found. 
>> This method relies on keeping the reference taken by the loop.
> 
> Sure. For the found node, that makes sense.
> 
> However, it also increments the refcount of all the parents, which does
> not seem correct to me, given they're not put on the return path, and a
> put of the found node won't decrement its parents refcounts, unless I
> have missed something.
> 

Hmm, yes. The parent refcounts must be decremented. 

> So I believe we are missing some of_node_put logic here.
> 
>> Taking this into account all of these conccinelle tests are bogus.
>> 
>> The DT internal method are not using the object model in an obvious manner
>> and applying these patches without vetting each and everyone is bound to
>> break things.
> 
> Agreed.
> 
> Thanks,
> Mark.
> --
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