Messages in this thread | | | Subject | Re: [PATCH] drm/imx: Fix of_node ref counting | From | Philipp Zabel <> | Date | Mon, 05 Sep 2016 10:01:56 +0200 |
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Hi Christophe,
Am Sonntag, den 04.09.2016, 08:45 +0200 schrieb Christophe JAILLET: > This code is spurious. > It takes a ref on a node, then call 'of_node_put' on it and then store > this node somewhere.
The node pointer is not stored. Note that np is not dereferenced at all, we just compare the pointer value against dev->of_node. It doesn't matter whether we drop the reference before or after that.
> It is likely that taking the ref on the parent node and releasing the child > node was expected instead.
Initially, np is assigned to the void *data parameter. The caller holds the reference to that, and we are not allowed to decrement its refcount (as of_get_next_parent does). Otherwise the iterator calling this match function would drop references of all the device_nodes it compares against.
> So, use 'of_get_next_parent' instead. It does all this in just one > function call. > > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > --- > Un-tested > --- > drivers/gpu/drm/imx/imx-drm-core.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/imx/imx-drm-core.c b/drivers/gpu/drm/imx/imx-drm-core.c > index 438bac8fbc2b..60fb388c80f8 100644 > --- a/drivers/gpu/drm/imx/imx-drm-core.c > +++ b/drivers/gpu/drm/imx/imx-drm-core.c > @@ -449,10 +449,8 @@ static int compare_of(struct device *dev, void *data) > } > > /* Special case for LDB, one device for two channels */ > - if (of_node_cmp(np->name, "lvds-channel") == 0) { > - np = of_get_parent(np); > - of_node_put(np); > - }
This could have been written as:
bool match;
/* Special case for LDB, one device for two channels */ if (of_node_cmp(np->name, "lvds-channel") == 0) { struct device_node *parent = of_get_parent(np);
match = dev->of_node == parent; of_node_put(parent); } else { match = dev->of_node == np; }
return match;
which does exactly the same. Maybe the reuse of np and the pointer comparison after of_node_put warrants a comment.
> + if (of_node_cmp(np->name, "lvds-channel") == 0) > + np = of_get_next_parent(np); > > return dev->of_node == np; > }
thanks Philipp
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