linux-kernel - Re: [PATCH 1/7] phy: brcmstb-sata: add missing of_node

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Date:	Tue, 17 Nov 2015 07:12:22 +0100 (CET)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	Brian Norris <computersforpeace@...il.com>
cc:	Julia Lawall <Julia.Lawall@...6.fr>,
	Kishon Vijay Abraham I <kishon@...com>,
	kernel-janitors@...r.kernel.org,
	Gregory Fong <gregory.0xf0@...il.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH 1/7] phy: brcmstb-sata: add missing of_node_put



On Mon, 16 Nov 2015, Brian Norris wrote:

> On Mon, Nov 16, 2015 at 12:33:14PM +0100, Julia Lawall wrote:
> > for_each_available_child_of_node performs an of_node_get on each iteration,
> > so a return from the middle of the loop requires an of_node_put.
> > 
> > A simplified version of the semantic patch that finds this problem is as
> > follows (http://coccinelle.lip6.fr):
> > 
> > // <smpl>
> > @@
> > expression root,e;
> > local idexpression child;
> > @@
> > 
> >  for_each_available_child_of_node(root, child) {
> >    ... when != of_node_put(child)
> >        when != e = child
> > (
> >    return child;
> > |
> > *  return ...;
> > )
> >    ...
> >  }
> > // </smpl>
> > 
> > Signed-off-by: Julia Lawall <Julia.Lawall@...6.fr>
> > 
> > ---
> 
> For this patch:
> 
> Acked-by: Brian Norris <computersforpeace@...il.com>
> 
> >  drivers/phy/phy-brcmstb-sata.c |   17 ++++++++++++-----
> >  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> [snip patch, which fixes of_node_put() handling for
> for_each_available_child_of_node() loop, which creates PHY devices with
> devm_phy_create()]
> 
> This reminds me of a potential problem I'm looking at in other
> subsystems: from code reading (I haven't seen any issues in practice,
> probably because I don't use OF_DYNAMIC) it looks like device-creating
> infrastructure like the PHY subsystem should be acquiring a reference to
> the device_node when they stash it away. But drivers/phy/phy-core.c does
> not do this, AFAICT.
> 
> See phy_create(), which does
> 
> 	phy->dev.of_node = node ?: dev->of_node;
> 
> and later might reuse this of_node pointer, even though it never called
> of_node_get() on this node.
> 
> Potential patch to fix this (not tested).
> 
> Signed-off-by: Brian Norris <computersforpeace@...il.com>
> 
> 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?

julia

>  	phy->id = id;
>  	phy->ops = ops;
>  
> @@ -726,6 +727,7 @@ struct phy *phy_create(struct device *dev, struct device_node *node,
>  	return phy;
>  
>  put_dev:
> +	of_node_put(phy->dev.of_node);
>  	put_device(&phy->dev);  /* calls phy_release() which frees resources */
>  	return ERR_PTR(ret);
>  
> @@ -775,6 +777,7 @@ EXPORT_SYMBOL_GPL(devm_phy_create);
>   */
>  void phy_destroy(struct phy *phy)
>  {
> +	of_node_put(phy->dev.of_node);
>  	pm_runtime_disable(&phy->dev);
>  	device_unregister(&phy->dev);
>  }
> --
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