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

[Andy Shevchenko]

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.

-- 
With Best Regards,
Andy Shevchenko