linux-kernel - Re: [PATCH] device property: Fix usecount for of_graph_get_port

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Date:   Fri, 28 Jul 2017 17:58:17 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Grant Likely <grant.likely@...aro.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>, Takashi Iwai <tiwai@...e.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Linux-ALSA <alsa-devel@...a-project.org>
Subject: Re: [PATCH] device property: Fix usecount for of_graph_get_port_parent()

On Fri, Jul 28, 2017 at 3:23 AM, Tony Lindgren <tony@...mide.com> wrote:
> * Tony Lindgren <tony@...mide.com> [170727 23:02]:
>> * Rob Herring <robh+dt@...nel.org> [170727 15:19]:
>> > On Thu, Jul 27, 2017 at 4:44 AM, Tony Lindgren <tony@...mide.com> wrote:
>> > > --- a/drivers/of/property.c
>> > > +++ b/drivers/of/property.c
>> > > @@ -708,6 +708,15 @@ struct device_node *of_graph_get_port_parent(struct device_node *node)
>> > >  {
>> > >         unsigned int depth;
>> > >
>> > > +       if (!node)
>> > > +               return NULL;
>> > > +
>> > > +       /*
>> > > +        * Preserve usecount for passed in node as of_get_next_parent()
>> > > +        * will do of_node_put() on it.
>> > > +        */
>> > > +       of_node_get(node);
>> >
>> > I think this messes up of_graph_get_remote_port_parent(). First it
>> > calls of_graph_get_remote_endpoint which returns the endpoint node
>> > with ref count incremented. Then you are incrementing it again here.
>>
>> Hmm OK looks like I missed that one. If we want to have
>> of_graph_get_port_parent not trash the node passed to it, we should
>> just change things there too:
>
> Found few more things to fix with git grep -C20 of_graph_get_port_parent,
> below is v2.
>
> Can you all prese review again and do some testing. I also fixed up
> audio-graph-scu-card but can't test that one.
>
> Regards,
>
> Tony
>
> 8< ------
> From tony Mon Sep 17 00:00:00 2001
> From: Tony Lindgren <tony@...mide.com>
> Date: Thu, 27 Jul 2017 01:30:16 -0700
> Subject: [PATCHv2] device property: Fix usecount for
>  of_graph_get_port_parent()
>
> Fix inconsistent use of of_graph_get_port_parent() where
> asoc_simple_card_parse_graph_dai() does of_node_get() before
> calling it while other callers do not. We can fix this by
> not trashing the node passed to of_graph_get_port_parent().
>
> Let's also make sure the callers have correct refcounts and remove
> related incorrect of_node_put() calls for of_for_each_phandle
> as that's done by of_phandle_iterator_next() except when
> we break out of the loop early.
>
> Let's fix both issues with a single patch to avoid kobject
> refcounts getting messed up more if two patches are merged
> separately.
>
> Otherwise strange issues can happen caused by memory corruption
> caused by too many kobject_del() calls such as:
>
> BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:747
> ...
> (___might_sleep)
> (__mutex_lock)
> (mutex_lock_nested)
> (kernfs_remove)
> (kobject_del)
> (kobject_put)
> (of_get_next_parent)
> (of_graph_get_port_parent)
> (asoc_simple_card_parse_graph_dai [snd_soc_simple_card_utils])
> (asoc_graph_card_probe [snd_soc_audio_graph_card])
>
> Fixes: 0ef472a973eb ("of_graph: add of_graph_get_port_parent()")
> Fixes: 2692c1c63c29 ("ASoC: add audio-graph-card support")
> Fixes: 1689333f8311 ("ASoC: simple-card-utils: add asoc_simple_card_parse_graph_dai()")
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Takashi Iwai <tiwai@...e.com>
> Cc: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
> Cc: alsa-devel@...a-project.org
> Signed-off-by: Tony Lindgren <tony@...mide.com>
> ---
>  drivers/of/property.c                    | 17 +++++++++++++++--
>  sound/soc/generic/audio-graph-card.c     | 10 +++++-----
>  sound/soc/generic/audio-graph-scu-card.c | 15 +++++++++------
>  sound/soc/generic/simple-card-utils.c    |  8 +++-----
>  sound/soc/soc-core.c                     |  2 ++
>  5 files changed, 34 insertions(+), 18 deletions(-)

LGTM. I'm assuming this will go thru ALSA tree.

Reviewed-by: Rob Herring <robh@...nel.org>

Rob