linux-kernel - Re: [PATCH 3/9] drm/msm: fix OF child-node lookup

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Date:   Wed, 22 Aug 2018 09:41:04 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH 3/9] drm/msm: fix OF child-node lookup

On Wed, Aug 22, 2018 at 5:57 AM Johan Hovold <johan@...nel.org> wrote:
>
> Use the new of_get_compatible_child() helper to lookup the legacy
> pwrlevels child node instead of using of_find_compatible_node(), which
> searches the entire tree and thus can return an unrelated (i.e.
> non-child) node.
>
> This also addresses a potential use-after-free (e.g. after probe
> deferral) as the tree-wide helper drops a reference to its first
> argument (i.e. the probed device's node).
>
> While at it, also fix the related child-node reference leak.
>
> Fixes: e2af8b6b0ca1 ("drm/msm: gpu: Use OPP tables if we can")
> Cc: stable <stable@...r.kernel.org>     # 4.12
> Cc: Jordan Crouse <jcrouse@...eaurora.org>
> Cc: Rob Clark <robdclark@...il.com>
> Cc: David Airlie <airlied@...ux.ie>
> Signed-off-by: Johan Hovold <johan@...nel.org>
> ---
>  drivers/gpu/drm/msm/adreno/adreno_gpu.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> index da1363a0c54d..93d70f4a2154 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> @@ -633,8 +633,7 @@ static int adreno_get_legacy_pwrlevels(struct device *dev)
>         struct device_node *child, *node;
>         int ret;
>
> -       node = of_find_compatible_node(dev->of_node, NULL,
> -               "qcom,gpu-pwrlevels");
> +       node = of_get_compatible_child(dev->of_node, "qcom,gpu-pwrlevels");

Not really your problem, but this is undocumented and a downstream
binding. There's been OPP support in addition for more than a year
now, we should just remove this code IMO. For some reason though, no
one updated the 8064 dts though.

Rob