linux-kernel - Re: [PATCH 1/3] backlight: as3711

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Date:   Mon, 20 Nov 2017 11:49:40 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Johan Hovold <johan@...nel.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable <stable@...r.kernel.org>,
        Guennadi Liakhovetski <g.liakhovetski@....de>
Subject: Re: [PATCH 1/3] backlight: as3711_bl: fix device-tree node lookup

On Wed, Nov 15, 2017 at 03:39:09PM +0100, Johan Hovold wrote:
> On Wed, Nov 15, 2017 at 02:32:11PM +0000, Lee Jones wrote:
> > On Wed, 15 Nov 2017, Johan Hovold wrote:
> > 
> > > On Tue, Nov 14, 2017 at 07:48:09PM +0000, Daniel Thompson wrote:
> > > > On 14/11/17 18:05, Johan Hovold wrote:
> > > > > On Mon, Nov 13, 2017 at 02:16:09PM +0000, Daniel Thompson wrote:
> > > > >> On 13/11/17 10:20, Johan Hovold wrote:
> > > > >>> Fix child-node lookup during probe, which ended up searching the whole
> > > > >>> device tree depth-first starting at the parent rather than just matching
> > > > >>> on its children.
> > > > >>>
> > > > >>> To make things worse, the parent mfd node was also prematurely freed.
> > > > >>>
> > > > >>> Note that the nodes returned from the two calls to of_parse_phandle()
> > > > >>> are also leaking, but fixing that is a bit more involved as pointers to
> > > > >>> node fields are being stored for later use.
> > > > >>
> > > > >> Is using a devm_kstrdup() to remember the full_name sufficient so get
> > > > >> each of the FIXMEs cleaned up as well?
> > > > > 
> > > > > Yeah, that may be sufficient, but looking closer at this now, it seems
> > > > > the name pointers (su1_fb and su2_fb) are only used as booleans, and the
> > > > > fb_name pointer in struct as3711_bl_data is never used at all.
> > > > > 
> > > > > So cleaning that up somehow (e.g. and maybe even dropping non-dt
> > > > > probing) would also work.
> > > > > 
> > > > > But since this is a separate, and less critical issue, I think it needs
> > > > > to be done as a follow up to this one.
> > > > 
> > > > To be honest it was adding the separate and less critical FIXMEs into 
> > > > the patches that attracted my attention in the first place. ;-)
> > > 
> > > Heh. Since I was touching those error paths, I at least wanted to record
> > > somehow there were further issues to be addressed. But feel free to drop
> > > the FIXMEs if you prefer.
> > 
> > In my experience FIXME's tend not to get addressed:
> > 
> > $ git grep -i fixme | wc -l
> > 4431
> > 
> > Submit patches instead. :)
> 
> There may be some truth to that, but I still think it's better to mark
> what is broken (especially since a leaked node is no big deal in this
> case) than to just ignore and forget about it.

I just sent a v2 including a new patch fixing these node leaks instead
of just flagging them. The driver really had no business storing those
node full_name fields in the first place.

Johan