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

[Xu Yang]

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 :)

Thanks,
Xu Yang