Hi Sakari,
On 2017-08-21 22:03:02 +0300, Sakari Ailus wrote:
> Hi Niklas,
>
> Niklas Söderlund wrote:
> > Hi Sakari,
> >
> > On 2017-08-21 16:30:17 +0300, Sakari Ailus wrote:
> > > Hi Niklas,
> > >
> > > Niklas Söderlund wrote:
> > > > Using CONFIG_OF_DYNAMIC=y uncovered an imbalance in the usecount of the
> > > > node being passed to of_fwnode_graph_get_port_parent(). Preserve the
> > > > usecount just like it is done in of_graph_get_port_parent().
> > >
> > > The of_fwnode_graph_get_port_parent() is called by
> > > fwnode_graph_get_port_parent() which obtains the port node through
> > > fwnode_get_parent(). If you take a reference here, calling
> > > fwnode_graph_get_port_parent() will end up incrementing the port node's use
> > > count. In other words, my understanding is that dropping the reference to
> > > the port node isn't a problem but intended behaviour here.
> >
> > I'm not sure but I don't think the usecount will be incremented, without
> > this patch I think it's decremented by one instead. Lets look at the
> > code starting with fwnode_graph_get_port_parent().
> >
> > struct fwnode_handle *
> > fwnode_graph_get_port_parent(struct fwnode_handle *endpoint)
> > {
> > struct fwnode_handle *port, *parent;
> >
> > Increment usecount by 1
> >
> > port = fwnode_get_parent(endpoint);
> > parent = fwnode_call_ptr_op(port, graph_get_port_parent);
> >
> > Decrement usecount by 1
> >
> > fwnode_handle_put(port); << Usecount -1
>
> Here it is; this is the one I missed.
>
> I spotted something else, too. Look at of_graph_get_port_parent(); it
> appears to decrement the use count of the node passed to it, too:
>
> struct device_node *of_graph_get_port_parent(struct device_node *node)
> {
> unsigned int depth;
>
> /* Walk 3 levels up only if there is 'ports' node. */
> for (depth = 3; depth && node; depth--) {
> node = of_get_next_parent(node);
> if (depth == 2 && of_node_cmp(node->name, "ports"))
> break;
> }
> return node;
> }
> EXPORT_SYMBOL(of_graph_get_port_parent);
>
> I think you'd need to of_node_get(node) first. I think it'd be good to
> address this at the same time.
Your tree is old :-)
I did check of_graph_get_port_parent() when looking for how this was
handled elsewhere in the kernel. But I did not realise that the fix was
accepted after 4.13-rc1 so I did not mention that this was just a copy
of that fix in the patch description. For reference see
c0a480d1acf7dc18 ("device property: Fix usecount for of_graph_get_port_parent()")
>
> One could claim the original design principle has truly been adopted in the
> fwnode variant of the function. X-)
Yes and I adopted the same fix for the original :-)
>
> On your original patch --- could you replace of_get_next_parent() by
> of_get_parent()? In that case it won't drop the reference to the parent,
> i.e. does what's required.
I do however think this is a much nicer solution. So I would still be
inclined to send a v2 whit this change instead. Which solution would you
prefer?
>
> >
> > return parent;
> > }
> >
> > Here it looks like the counting is correct and balanced. But without
> > this patch it's in this function 'fwnode_handle_put(port)' which
> > triggers the error which this patch aims to fix. Lets look at
> > of_fwnode_graph_get_port_parent() which in my case is what is called by
> > the fwnode_call_ptr_op().
> >
> > static struct fwnode_handle *
> > of_fwnode_graph_get_port_parent(struct fwnode_handle *fwnode)
> > {
> > struct device_node *np;
> >
> > Here in of_get_next_parent() the usecount is decremented by 1 and the
> > parents usecount is incremented by 1. So for our node node which passed
> > in from fwnode_graph_get_port_parent() (where it's named 'port') will be
> > decremented by 1.
> >
> > /* Get the parent of the port */
> > np = of_get_next_parent(to_of_node(fwnode));
> > if (!np)
> > return NULL;
> >
> > /* Is this the "ports" node? If not, it's the port parent. */
> > if (of_node_cmp(np->name, "ports"))
> > return of_fwnode_handle(np);
> >
> > return of_fwnode_handle(of_get_next_parent(np));
> > }
> >
> > So unless I miss something I do think this patch is needed to restore
> > balance to the usecount of the node being passed to
> > of_fwnode_graph_get_port_parent(). Or maybe I have misunderstood
> > something?
> >
> > >
> > > I wonder if I miss something.
> >
> > I also wonder what I missed :-)
> >
> > >
> > > >
> > > > Fixes: 3b27d00e7b6d7c88 ("device property: Move fwnode graph ops to firmware specific locations")
> > > > Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
> > > > ---
> > > > drivers/of/property.c | 6 ++++++
> > > > 1 file changed, 6 insertions(+)
> > > >
> > > > diff --git a/drivers/of/property.c b/drivers/of/property.c
> > > > index 067f9fab7b77c794..637dcb4833e2af60 100644
> > > > --- a/drivers/of/property.c
> > > > +++ b/drivers/of/property.c
> > > > @@ -922,6 +922,12 @@ of_fwnode_graph_get_port_parent(struct fwnode_handle *fwnode)
> > > > {
> > > > struct device_node *np;
> > > >
> > > > + /*
> > > > + * Preserve usecount for passed in node as of_get_next_parent()
> > > > + * will do of_node_put() on it.
> > > > + */
> > > > + of_node_get(to_of_node(fwnode));
> > > > +
> > > > /* Get the parent of the port */
> > > > np = of_get_next_parent(to_of_node(fwnode));
> > > > if (!np)
> > > >
> > >
> > >
> > > --
> > > Sakari Ailus
> > > sakari.ailus@xxxxxxxxxxxxxxx
> >
>
>
> --
> Sakari Ailus
> sakari.ailus@xxxxxxxxxxxxxxx
--
Regards,
Niklas Söderlund
