From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sakari Ailus Subject: Re: [PATCH] device property: preserve usecount for node passed to of_fwnode_graph_get_port_parent() Date: Mon, 21 Aug 2017 22:03:02 +0300 Message-ID: <8e5d0f0b-de07-c25e-a6f9-cb2109e67cbe@linux.intel.com> References: <20170821125107.20746-1-niklas.soderlund+renesas@ragnatech.se> <282c50da-8927-d1fc-27e5-39b75f3ba564@linux.intel.com> <20170821140443.GA32709@bigcity.dyn.berto.se> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20170821140443.GA32709@bigcity.dyn.berto.se> Sender: linux-media-owner@vger.kernel.org To: =?UTF-8?Q?Niklas_S=c3=b6derlund?= Cc: devicetree@vger.kernel.org, linux-media@vger.kernel.org, Kieran Bingham , linux-renesas-soc@vger.kernel.org List-Id: devicetree@vger.kernel.org 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. One could claim the original design principle has truly been adopted in the fwnode variant of the function. X-) 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. > > 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 >>> --- >>> 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@linux.intel.com > -- Sakari Ailus sakari.ailus@linux.intel.com