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

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Message-ID: <20160510000243.GD15535@dtor-ws>
Date:	Mon, 9 May 2016 17:02:43 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	"H. Nikolaus Schaller" <hns@...delico.com>
Cc:	Fabio Estevam <fabio.estevam@...escale.com>,
	linux-input@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Discussions about the Letux Kernel 
	<letux-kernel@...nphoenux.org>, kernel@...a-handheld.com
Subject: Re: [Kernel] [PATCH 1/5] input: twl6040-vibra: fix DT node memory
 management

On Sun, May 08, 2016 at 08:49:27AM +0200, H. Nikolaus Schaller wrote:
> Hi Dmitry,
> 
> > Am 20.04.2016 um 11:03 schrieb H. Nikolaus Schaller <hns@...delico.com>:
> > 
> > 
> >> 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.
> 
> Any progress on this?

I'll apply your patch for now and then will try to get mine worked in.

Thanks.

-- 
Dmitry