Re: [PATCH] net: ethernet: bgmac-platform: fix an OF node reference leak

On Fri, Dec 13, 2024 at 01:04:42PM +0100, Andrew Lunn wrote:

quoted

Hi Joe,

I agree this is a problem and that it was introduced by the
cited commit. But I wonder if we can consider a different approach.

I would suggest that rather than using __free the node is explicitly
released. Something like this (untested):

	struct device_node *phy_node;

	...

	phy_node = of_parse_phandle(np, "phy-handle", 0);
	if (phy_node) {
		of_node_put(phy_node);
		bgmac->phy_connect = platform_phy_connect;
	} ...

That is, assuming that it is safe to release phy_node so early.
If not, some adjustment should be made to when of_node_put()
is called.

This is for several reasons;

1. I could be wrong, but I believe your patch kfree's phy_node,
   but my understanding is that correct operation is to call
   of_node_put().

Hi Simon

I _think_ that is wrong. More of the magic which i don't really
like. The cleanup subsystem has to be taught all the types, and what
operation to perform for each type. Despite the name __free(), i think
it does actually call of_node_put(). The magic would be more readable
if it was actually __put(), not __free().

Thanks, TIL.

quoted

2. More importantly, there is a preference in Newkorking code
   not to use __free and similar constructs.

     "Low level cleanup constructs (such as __free()) can be used when
      building APIs and helpers, especially scoped iterators. However,
      direct use of __free() within networking core and drivers is
      discouraged. Similar guidance applies to declaring variables
      mid-function.

And this is a good example of why.

	Andrew