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    SubjectRe: [PATCH] of: resolver: Add missing of_node_put


    On Wed, 27 Jan 2016, Pantelis Antoniou wrote:

    > Hi Mark,
    >
    > > On Jan 27, 2016, at 18:21 , Mark Rutland <mark.rutland@arm.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@arm.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@gmail.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 there should be if (found != child) of_node_put(child); ? Another
    option would be to duplicate the test and avoid the recursive call.

    julia

    > > 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.
    > > --
    > > To unsubscribe from this list: send the line "unsubscribe devicetree" in
    > > the body of a message to majordomo@vger.kernel.org
    > > More majordomo info at http://vger.kernel.org/majordomo-info.html
    >
    >

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