linux-kernel - Re: [PATCH v2 4/8] drm/msm/dpu: Disallow unallocated resources to be returned

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Message-ID: <b415a91d-f804-1fec-52dd-4124d3f1e583@linaro.org>
Date:   Mon, 9 Jan 2023 01:28:52 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        phone-devel@...r.kernel.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Vinod Koul <vkoul@...nel.org>
Cc:     ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Stephen Boyd <swboyd@...omium.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Jessica Zhang <quic_jesszhan@...cinc.com>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Jani Nikula <jani.nikula@...el.com>,
        sunliming <sunliming@...inos.cn>,
        Sam Ravnborg <sam@...nborg.org>,
        Haowen Bai <baihaowen@...zu.com>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Loic Poulain <loic.poulain@...aro.org>,
        Vinod Polimera <quic_vpolimer@...cinc.com>,
        Douglas Anderson <dianders@...omium.org>,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Drew Davenport <ddavenport@...omium.org>
Subject: Re: [PATCH v2 4/8] drm/msm/dpu: Disallow unallocated resources to be
 returned

On 22/12/2022 01:19, Marijn Suijten wrote:
> In the event that the topology requests resources that have not been
> created by the system (because they are typically not represented in
> dpu_mdss_cfg ^1), the resource(s) in global_state (in this case DSC
> blocks) remain NULL but will still be returned out of
> dpu_rm_get_assigned_resources, where the caller expects to get an array
> containing num_blks valid pointers (but instead gets these NULLs).
> 
> To prevent this from happening, where null-pointer dereferences
> typically result in a hard-to-debug platform lockup, num_blks shouldn't
> increase past NULL blocks and will print an error and break instead.
> After all, max_blks represents the static size of the maximum number of
> blocks whereas the actual amount varies per platform.
> 
> ^1: which can happen after a git rebase ended up moving additions to
> _dpu_cfg to a different struct which has the same patch context.
> 
> Fixes: bb00a452d6f7 ("drm/msm/dpu: Refactor resource manager")
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c | 5 +++++
>   1 file changed, 5 insertions(+)

I think the patch is not fully correct. Please check resource 
availability during allocation. I wouldn't expect an error from 
get_assigned_resources because of resource exhaustion.

-- 
With best wishes
Dmitry