linux-kernel - Re: [PATCH] bus: vexpress-config: Add missing of_node

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Message-ID: <20160125125104.GD1194@e106497-lin.cambridge.arm.com>
Date:	Mon, 25 Jan 2016 12:51:05 +0000
From:	liviu.dudau@....com
To:	Julia Lawall <julia.lawall@...6.fr>
Cc:	Amitoj Kaur Chawla <amitoj1606@...il.com>, sudeep.holla@....com,
	lorenzo.pieralisi@....com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] bus: vexpress-config: Add missing of_node_put

On Mon, Jan 25, 2016 at 01:24:44PM +0100, Julia Lawall wrote:
> 
> 
> On Mon, 25 Jan 2016, liviu.dudau@....com wrote:
> 
> > On Fri, Jan 22, 2016 at 11:38:38PM +0530, Amitoj Kaur Chawla wrote:
> > > for_each_compatible_node performs an of_node_get on each iteration, so
> > > to break out of the loop an of_node_put is required.
> > >
> > > Found using Coccinelle. The semantic patch used for this is as follows:
> > >
> > > // <smpl>
> > > @@
> > > expression e;
> > > local idexpression n;
> > > @@
> > >
> > >  for_each_compatible_node(n, ...) {
> > >    ... when != of_node_put(n)
> > >        when != e = n
> > > (
> > >    return n;
> > > +  of_node_put(n);
> > > ?  return ...;
> > > )
> > >    ...
> > >  }
> > > // </smpl>
> > >
> > > Signed-off-by: Amitoj Kaur Chawla <amitoj1606@...il.com>
> >
> > Hi Amitoj,
> >
> > > ---
> > >  drivers/bus/vexpress-config.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/bus/vexpress-config.c b/drivers/bus/vexpress-config.c
> > > index 6575c0f..c3cb76b 100644
> > > --- a/drivers/bus/vexpress-config.c
> > > +++ b/drivers/bus/vexpress-config.c
> > > @@ -192,8 +192,10 @@ static int __init vexpress_config_init(void)
> > >  	/* Need the config devices early, before the "normal" devices... */
> > >  	for_each_compatible_node(node, NULL, "arm,vexpress,config-bus") {
> > >  		err = vexpress_config_populate(node);
> > > -		if (err)
> > > +		if (err) {
> > > +			of_node_put(node);
> > >  			break;
> > > +		}
> >
> > This automatically generated patch only solves half of the problem (for the error
> > path).
> >
> > >  	}
> > >
> > >  	return err;
> > > --
> > > 1.9.1
> > >
> >
> > I feel that a better patch would be the following, where the node is released
> > regardless of the result of vexpress_config_populate().
> >
> > --8<--------------------------------------------------------------------------
> > diff --git a/drivers/bus/vexpress-config.c b/drivers/bus/vexpress-config.c
> > index 6575c0f..c57453d 100644
> > --- a/drivers/bus/vexpress-config.c
> > +++ b/drivers/bus/vexpress-config.c
> > @@ -192,6 +192,7 @@ static int __init vexpress_config_init(void)
> >  	/* Need the config devices early, before the "normal" devices... */
> >  	for_each_compatible_node(node, NULL, "arm,vexpress,config-bus") {
> >  		err = vexpress_config_populate(node);
> > +		of_node_put(node);
> 
> This is not correct.  for_each_compatible_node will do the free if you go
> around the loop.  This change would lead to a double free in the non error
> case.

You are correct and I withdraw my patch.

For the original patch:

Acked-by: Liviu Dudau <Liviu.Dudau@....com>

Best regards,
Liviu

> 
> julia
> 
> >  		if (err)
> >  			break;
> >  	}
> > -->8--------------------------------------------------------------------------

-- 
====================
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