linux-kernel - Re: [PATCH v2] device property: fix of node refcount leak in fwnode_graph_get_next

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Message-ID: <Y3zXjpY2/Le/3J9q@smile.fi.intel.com>
Date:   Tue, 22 Nov 2022 16:07:10 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        djrscally@...il.com, heikki.krogerus@...ux.intel.com,
        sakari.ailus@...ux.intel.com, gregkh@...uxfoundation.org,
        rafael@...nel.org
Subject: Re: [PATCH v2] device property: fix of node refcount leak in
 fwnode_graph_get_next_endpoint()

On Tue, Nov 22, 2022 at 09:41:28PM +0800, Yang Yingliang wrote:
> On 2022/11/22 21:16, Andy Shevchenko wrote:
> > On Tue, Nov 22, 2022 at 09:12:41PM +0800, Yang Yingliang wrote:
> > > On 2022/11/22 20:54, Andy Shevchenko wrote:
> > > > On Tue, Nov 22, 2022 at 08:00:39PM +0800, Yang Yingliang wrote:

...

> > > > It seems too complicated for the simple fix.
> > > > 
> > > > As I said, just drop const qualifier and add fwnode_handle_get() in the 'else'
> > > > branch. This will allow you to drop if (prev) at the end.
> > > fwnode is const, fwnode_handle_get doesn't accept this type.
> > I'm talking about parent.
> You suggested this:
> 
> "Instead you might consider to replace
> 
> 	parent = fwnode;
> 
> by
> 
> 	parent = fwnode_handle_get(fwnode);"
> 
> 
> It has compile warning:
> drivers/base/property.c: In function ‘fwnode_graph_get_next_endpoint’:
> drivers/base/property.c:1004:30: warning: passing argument 1 of ‘fwnode_handle_get’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
>    parent = fwnode_handle_get(fwnode);
>                               ^~~~~~
> drivers/base/property.c:809:63: note: expected ‘struct fwnode_handle *’ but argument is of type ‘const struct fwnode_handle *’
>  struct fwnode_handle *fwnode_handle_get(struct fwnode_handle *fwnode)
> 
> ~~~~~~~~~~~~~~~~~~~~~~^~~~~~

I see what you mean. Thank you for clarification.

So, it seems a bit twisted.

If prev == NULL, can the

        ep = fwnode_call_ptr_op(parent, graph_get_next_endpoint, NULL);

return NULL?

If no, we may move this case directly to the 'else' branch and return from there.

-- 
With Best Regards,
Andy Shevchenko