linux-kernel - Re: [PATCH] thermal: tegra: delete unneeded of_node

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Date:   Tue, 5 Dec 2017 07:17:02 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Eduardo Valentin <edubezval@...il.com>
cc:     Jon Hunter <jonathanh@...dia.com>, Zhang Rui <rui.zhang@...el.com>,
        kernel-janitors@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thermal: tegra: delete unneeded of_node_put



On Mon, 4 Dec 2017, Eduardo Valentin wrote:

> On Mon, Jul 17, 2017 at 04:42:38PM +0200, Julia Lawall wrote:
> >
> >
> > On Mon, 17 Jul 2017, Jon Hunter wrote:
> >
> > >
> > > On 15/07/17 09:42, Julia Lawall wrote:
> > > > Device node iterators perform an of_node_put on each iteration, so putting
> > > > an of_node_put before a continue results in a double put.
> > > >
> > > > The semantic match that finds this problem is as follows
> > > > (http://coccinelle.lip6.fr):
> > > >
> > > > // <smpl>
> > > > @@
> > > > expression e1;
> > > > local idexpression child;
> > > > iterator name for_each_child_of_node;
> > > > @@
> > > >
> > > >  for_each_child_of_node(e1,child) {
> > > >    ... when != of_node_get(child)
> > > > *  of_node_put(child);
> > > >    ...
> > > > *  continue;
> > > > }
> > > > // </smpl>
> > > >
> > > > Furthermore, the call to thermal_of_cooling_device_register immediately
> > > > calls __thermal_cooling_device_register with the same arguments.  The
> > > > latter function stores the device node argument, which is the second
> > > > argument of for_each_child_of_node, in the returned thermal_cooling_device
> > > > structure.  This returned structure is then stored in the cdev field of
> > > > stc.  Thus it seems that the second argument of for_each_child_of_node
> > > > escapes the scope of the for_each_child_of_node, so an explicit of_node_get
> > > > on success of thermal_of_cooling_device_register is also needed.
> > > >
> > > > Signed-off-by: Julia Lawall <Julia.Lawall@...6.fr>
> > > >
> > > > ---
> > > >  drivers/thermal/tegra/soctherm.c |    2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/thermal/tegra/soctherm.c b/drivers/thermal/tegra/soctherm.c
> > > > index 7d2db23..10f4fdd 100644
> > > > --- a/drivers/thermal/tegra/soctherm.c
> > > > +++ b/drivers/thermal/tegra/soctherm.c
> > > > @@ -1014,7 +1014,6 @@ static void soctherm_init_hw_throt_cdev(struct platform_device *pdev)
> > > >  		tcd = thermal_of_cooling_device_register(np_stcc,
> > > >  							 (char *)name, ts,
> > > >  							 &throt_cooling_ops);
> > > > -		of_node_put(np_stcc);
> > > >  		if (IS_ERR_OR_NULL(tcd)) {
> > > >  			dev_err(dev,
> > > >  				"throttle-cfg: %s: failed to register cooling device\n",
> > > > @@ -1022,6 +1021,7 @@ static void soctherm_init_hw_throt_cdev(struct platform_device *pdev)
> > > >  			continue;
> > > >  		}
> > > >
> > > > +		of_node_get(np_stcc);
> > > >  		stc->cdev = tcd;
> > > >  		stc->init = true;
> > > >  	}
> > >
> > > Thanks for fixing this. However, I am wondering if it is better for the
> > > 'of_node_get' to be placed within the
> > > thermal_of_cooling_device_register() function as it seems a bit odd if
> > > the caller needs to know that this is being stored for later use.
> > >
> > > Also, taking a quick look, I see a couple other drivers calling
> > > thermal_of_cooling_device_register() and they are also not calling
> > > of_node_get on success. So it maybe easier to fix placing it in the
> > > thermal_of_cooling_device_register() function.
> >
> > I'm not an expert, but I had the impression that from some call sites, the
> > get would have been done already, because the argument is already stored
> > in some structure.  I can check more exhaustively.
>
> Julia, I agree with Jon here. Better if fixed in the API itself. Are you
> still planning on sending a fix for this?

This has fallen off my stack, and I'mnot sure that Ican get to it in the
short term.

julia