linux-kernel - Re: [PATCH 1/5] input: twl6040-vibra: fix DT node memory management

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Message-Id: <311BF03D-607A-410A-B678-9D7ED12A806F@goldelico.com>
Date:	Wed, 20 Apr 2016 11:03:01 +0200
From:	"H. Nikolaus Schaller" <hns@...delico.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Fabio Estevam <fabio.estevam@...escale.com>,
	Peter Ujfalusi <peter.ujfalusi@...com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel@...a-handheld.com, letux-kernel@...nphoenux.org
Subject: Re: [PATCH 1/5] input: twl6040-vibra: fix DT node memory management


> Am 19.04.2016 um 19:06 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
> 
> On Tue, Apr 19, 2016 at 09:43:08AM +0200, H. Nikolaus Schaller wrote:
>> 
>>> Am 18.04.2016 um 23:22 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
>>> 
>>> On Mon, Apr 18, 2016 at 09:55:37PM +0200, H. Nikolaus Schaller wrote:
>>>> commit e7ec014a47e4 ("Input: twl6040-vibra - update for device tree support")
>>>> 
>>>> made the separate vibra DT node to a subnode of the twl6040.
>>>> 
>>>> It now calls of_find_node_by_name() to locate the "vibra" subnode.
>>>> This function has a side effect to call of_node_put on() for the twl6040
>>>> parent node passed in as a parameter. This causes trouble later on.
>>>> 
>>>> Solution: we must call of_node_get() before of_find_node_by_name()
>>> 
>>> God, what messed up API.
>> 
>> Yes, indeed. It is opposite to the usual object ownership rule that the code
>> fragment that asks for a handle has to release it.
>> 
>> Usually it does not become obvious because often CONFIG_OF_DYNAMIC=n.
>> This disables all of_node refcounting completely so such bugs remain unnoticed.
>> 
>>> Any chance we can make it a bit more sane and
>>> not drop the reference inside it instead?
>> 
>> Well, if you want to change ~2000 files, test on all platforms and ask Linus
>> for agreement?
> 
> It's not that bad, let's see what DT maintainers say to the patch I
> posted...

Thanks! Would make me more happy a well.

Nikolaus