linux-kernel - Re: [RFC/PATCH] of: of_find_node_by_name - stop dropping reference to 'from' node

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Date:	Thu, 21 Apr 2016 15:35:16 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	Rob Herring <robh+dt@...nel.org>, Tony Lindgren <tony@...mide.com>,
	Scott Wood <oss@...error.net>,
	Kumar Gala <galak@...nel.crashing.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnd Bergmann <arnd@...db.de>,
	Grant Likely <grant.likely@...aro.org>,
	Jingoo Han <jingoohan1@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	"H. Nikolaus Schaller" <hns@...delico.com>,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [RFC/PATCH] of: of_find_node_by_name - stop dropping reference
 to 'from' node

On 4/19/2016 10:05 AM, Dmitry Torokhov wrote:
> Majority of the callers of of_find_node_by_name() do not expect that it
> will drop reference to the 'from' node if it was passed in, causing
> potential refcount underflows, etc, so let's stop doing this.
> 
> Most of the callers that were handling dropping of reference done by
> of_find_node_by_name() actually wanted for_each_node_by_name() instead.
> 
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> ---
> 
> If this is acceptable I can make changes to other of_find_node_*()
> methods...

No.  It is correct for of_find_by_name() to call of_node_put() for
the from argument.  The callers should be fixed.

-Frank

> 
>  arch/arm/mach-omap2/omap_hwmod_3xxx_data.c |  2 ++
>  arch/powerpc/platforms/83xx/mpc832x_mds.c  |  2 +-
>  arch/powerpc/platforms/83xx/mpc832x_rdb.c  |  2 +-
>  arch/powerpc/platforms/83xx/mpc836x_mds.c  |  2 +-
>  arch/powerpc/platforms/cell/interrupt.c    |  3 +--
>  arch/powerpc/platforms/cell/setup.c        |  3 +--
>  arch/powerpc/platforms/cell/spider-pic.c   |  3 +--
>  arch/powerpc/platforms/powermac/feature.c  |  2 +-
>  arch/powerpc/platforms/powermac/pic.c      |  2 --
>  drivers/input/misc/twl4030-vibra.c         |  8 +-------
>  drivers/of/base.c                          |  3 +--
>  drivers/pci/hotplug/rpadlpar_core.c        |  4 ++--
>  drivers/video/backlight/tps65217_bl.c      |  4 ++--
>  include/linux/of.h                         | 12 +++++++++---
>  14 files changed, 24 insertions(+), 28 deletions(-)

< snip >

> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index b299de2..45fc458 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -826,7 +826,7 @@ EXPORT_SYMBOL(of_find_node_opts_by_path);
>   *	@from:	The node to start searching from or NULL, the node
>   *		you pass will not be searched, only the next one
>   *		will; typically, you pass what the previous call
> - *		returned. of_node_put() will be called on it
> + *		returned.
>   *	@name:	The name string to match against
>   *
>   *	Returns a node pointer with refcount incremented, use
> @@ -843,7 +843,6 @@ struct device_node *of_find_node_by_name(struct device_node *from,
>  		if (np->name && (of_node_cmp(np->name, name) == 0)
>  		    && of_node_get(np))
>  			break;
> -	of_node_put(from);
>  	raw_spin_unlock_irqrestore(&devtree_lock, flags);
>  	return np;
>  }

< snip >