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

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Message-ID: <20160419170637.GB2881@dtor-ws>
Date:	Tue, 19 Apr 2016 10:06:37 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	"H. Nikolaus Schaller" <hns@...delico.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

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...

-- 
Dmitry