Re: [PATCH v3 0/2] device property: fix child iteration issues with secondary fwnodes

[Andy Shevchenko]

On Mon, Jun 08, 2026 at 10:41:45AM +0800, Xu Yang wrote:
> On Fri, Jun 05, 2026 at 06:52:49PM +0300, Andy Shevchenko wrote:
> > On Fri, Jun 05, 2026 at 06:07:41PM +0300, Andy Shevchenko wrote:
> > > On Fri, Jun 05, 2026 at 06:31:16PM +0800, Xu Yang wrote:
> > > > This series fixes two issues in the fwnode child iteration logic when
> > > > a secondary fwnode is present.
> > > > 
> > > > The first issue is  a refcount imbalance in software_node_get_next_child().
> > > > When a software node is used as a secondary fwnode, the iteration code may
> > > > incorrectly decrement the refcount of child nodes that do not belong to the
> > > > software node hierarchy. This results in refcount underflow and possible
> > > > use-after-free.
> > > > 
> > > > The second issue is an infinite loop in fwnode_for_each_child_node(), caused
> > > > by improper handling of iteration state across primary and secondary fwnodes.
> > > > When iterating over children from both primary and secondary fwnodes, the code
> > > > may incorrectly resume iteration from the primary fwnode even when the current
> > > > child belongs to the secondary, leading to repeated traversal and a loop.
> > > > 
> > > > Both issues are triggered when mixing different fwnode types through the
> > > > secondary mechanism, and stem from incorrect assumptions about ownership
> > > > and traversal context of child nodes.
> > > 
> > > > ---
> > > > Changes in v3:
> > > > - remove software node patch 
> > > 
> > > Hmm... Maybe I was unclear. My question was to investigate the way to actually
> > > move software node to use the swnode APIs (and not fwnode ones) and be on par
> > > with what OF code does. This series does the opposite and adds a hack to the
> > > next_child implementation.
> > > 
> > > > - add a kunit test case suggested by Andy Shevchenko
> > > 
> > > But thanks for the test case!
> > 
> > I'm preparing another patch (just a clean up) and I see that your test cases
> > indeed fail without any other patch being applied. Also noticed that the test
> > cases are not fully compliant with the requirement of the "primary"/"secondary"
> > fwnode flavours. But this doesn't affect the execution.
> > 
> > I will play more with this to understand the problem better.
> 
> OK. Suggestions on the fwnode flavours would be appreciated :)

I think your approach is what we should go with. I will send a v4 with my tags
and some amendments.

-- 
With Best Regards,
Andy Shevchenko