[PATCH] drm/imx: Fix of_node ref counting
Am Montag, den 05.09.2016, 10:01 +0200 schrieb Philipp Zabel:
> 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
> > ---
> > 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.
Actually, maybe we should just do
- if (of_node_cmp(np->name, "lvds-channel") == 0) {
- np = of_get_parent(np);
- of_node_put(np);
- }
+ if (of_node_cmp(np->name, "lvds-channel") == 0)
+ np = np->parent;
regards
Philipp
[PATCH] drm/imx: Fix of_node ref counting
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
> ---
> 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
[PATCH] drm/imx: Fix of_node ref counting
This code is spurious.
It takes a ref on a node, then call 'of_node_put' on it and then store
this node somewhere.
It is likely that taking the ref on the parent node and releasing the child
node was expected instead.
So, use 'of_get_next_parent' instead. It does all this in just one
function call.
Signed-off-by: Christophe JAILLET
---
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);
- }
+ if (of_node_cmp(np->name, "lvds-channel") == 0)
+ np = of_get_next_parent(np);
return dev->of_node == np;
}
--
2.7.4
