linux-kernel - Re: [PATCH] powermac: Call of_node_put(bk_node) only once in pmac_has_backlight

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Message-ID: <34233c4c-1f61-4bc6-aeca-9f5faba8509e@stanley.mountain>
Date: Thu, 3 Oct 2024 08:56:43 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Markus Elfring <Markus.Elfring@....de>, linuxppc-dev@...ts.ozlabs.org,
	Jani Nikula <jani.nikula@...el.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Naveen N Rao <naveen@...nel.org>,
	Nicholas Piggin <npiggin@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH] powermac: Call of_node_put(bk_node) only once in
 pmac_has_backlight_type()

First of all, the change is wrong.  We can't dereference "prop" after calling
of_node_put().  You have to be a bit extra careful reviewing Markus's patches
because a lot of the rest of us have blocked these messages so you're on your
own in that way.

On Wed, Oct 02, 2024 at 10:43:46PM +0200, Christophe Leroy wrote:
> 
> 
> Le 02/10/2024 à 22:02, Markus Elfring a écrit :
> > From: Markus Elfring <elfring@...rs.sourceforge.net>
> > Date: Wed, 2 Oct 2024 21:50:27 +0200
> > 
> > An of_node_put(bk_node) call was immediately used after a pointer check
> > for an of_get_property() call in this function implementation.
> > Thus call such a function only once instead directly before the check.
> 
> It seems pointless to perform a put immediately after a get. Shouldn't
> of_find_property() be used instead ? And then of_property_read_string()
> would probably be better.
> 
> Maybe you can even use of_property_match_string().

The of_get_property() function doesn't do a get as in get/put, it just finds
the property and returns it.  It doesn't bump the reference count.  It's a
confusing name in that way.  The The of_node_put() pairs with
of_find_node_by_name().

regards,
dan carpenter