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

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Date:	Thu, 28 Jan 2016 12:36:31 +0100 (CET)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	Mark Rutland <mark.rutland@....com>
cc:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	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>
Subject: Re: [PATCH] of: resolver: Add missing of_node_put



On Thu, 28 Jan 2016, Mark Rutland wrote:

> On Wed, Jan 27, 2016 at 08:48:00PM +0100, Julia Lawall wrote:
> >
> >
> > On Wed, 27 Jan 2016, Pantelis Antoniou wrote:
> >
> > > 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:
> > > >>>> 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 there should be if (found != child) of_node_put(child); ?
>
> That would match the intended semantics, yes.

I don't think so.  I sent another mail with what seems like a better
solution (upping the reference count of the child that is selected).

julia