Re: [PATCH 1/7] phy: brcmstb-sata: add missing of_node_put

[Brian Norris <computersforpeace@gmail.com>]

On Tue, Nov 17, 2015 at 06:48:39PM +0100, Julia Lawall wrote:
> On Tue, 17 Nov 2015, Brian Norris wrote:
> > On Tue, Nov 17, 2015 at 07:12:22AM +0100, Julia Lawall wrote:
> > > On Mon, 16 Nov 2015, Brian Norris wrote:
> > > > diff --git a/drivers/phy/phy-core.c b/drivers/phy/phy-core.c
> > > > index fc48fac003a6..8df29caeeef9 100644
> > > > --- a/drivers/phy/phy-core.c
> > > > +++ b/drivers/phy/phy-core.c
> > > > @@ -697,6 +697,7 @@ struct phy *phy_create(struct device *dev, struct device_node *node,
> > > >  	phy->dev.class = phy_class;
> > > >  	phy->dev.parent = dev;
> > > >  	phy->dev.of_node = node ?: dev->of_node;
> > > > +	of_node_get(phy->dev.of_node);
> > >
> > > Why not put of_node_get around dev->of_node?
> >
> > Like this?
> >
> > 	phy->dev.of_node = node ?: of_node_get(dev->of_node);
> >
> > Or this?
> >
> > 	phy->dev.of_node = of_node_get(node ?: dev->of_node);
> >
> > The former wouldn't do what I proposed; if this PHY device is created
> > with a sub-node of 'dev' rather than dev->of_node, then the caller will
> > pass it in as the 2nd argument to phy_create (i.e., 'node'), and then I
> > expect it's the PHY core's responsibility to refcount it.
> >
> > I'd be fine with the latter. Looks a little better, I suppose.
> 
> I proposed it because I was worried that the of_node field could end up
> containing something that had been freed.  But probably this is not
> possible?

AIUI, the caller of phy_create() should already have a refcount on both
'dev->of_node' and 'node' (if applicable), so nobody should be freeing
it from underneath us right here. But *after* phy_create() returns,
there's no guarantee the caller will hold a reference for us.

So even if it's ever possible, I'd consider it a bug in the caller, not
in phy_create().

> If it is not possible, then the ?: in the function argument is
> probably a bit ugly...

OK, then I'll go with my first proposal.

> Is this something that should be checked for elsewhere?

I expect the same sort of problem shows up plenty of other places. I
don't think many people use CONFIG_OF_DYNAMIC, so the effects of these
failures probably aren't felt by many.

Brian