linux-kernel - Re: [PATCH v3] drm/msm/dpu: Disallow unallocated resources to be returned

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Message-ID: <82ef3c2a-ef54-8c39-2266-7e3b203f92d1@linaro.org>
Date:   Wed, 18 Jan 2023 03:30:20 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        phone-devel@...r.kernel.org
Cc:     ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Stephen Boyd <swboyd@...omium.org>,
        Vinod Koul <vkoul@...nel.org>,
        Drew Davenport <ddavenport@...omium.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] drm/msm/dpu: Disallow unallocated resources to be
 returned

On 10/01/2023 01:15, 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, until their allocation/assignment is being sanity-checked in
> "drm/msm/dpu: Reject topologies for which no DSC blocks are available")
> 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>
> ---
> 
> Changes since v2:
> - Dropped all 7 other patches that were queued for -next;
> - Reworded error message to clarify that the requested resource should
>    have already been allocated, rather than sounding like
>    dpu_rm_get_assigned_resources is (re)allocating/(re)assigning
>    resources here;
> - This patch is now (implicitly!) based after "drm/msm/dpu: Reject
>    topologies for which no DSC blocks are available", which should make
>    it impossible to reach this condition, making it more of a safeguard
>    in case of future code changes and/or hidden issues: and is more
>    clearly conveyed in the patch message as well.
> 
> v2: https://lore.kernel.org/linux-arm-msm/20221221231943.1961117-5-marijn.suijten@somainline.org/
> 
>   drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c | 5 +++++
>   1 file changed, 5 insertions(+)

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

-- 
With best wishes
Dmitry