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

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Date:   Thu, 22 Dec 2022 00:19:39 +0100
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     phone-devel@...r.kernel.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        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>,
        Marijn Suijten <marijn.suijten@...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: [PATCH v2 4/8] drm/msm/dpu: Disallow unallocated resources to be returned

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(+)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
index 73b3442e7467..8471d04bff50 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
@@ -660,6 +660,11 @@ int dpu_rm_get_assigned_resources(struct dpu_rm *rm,
 				  blks_size, enc_id);
 			break;
 		}
+		if (!hw_blks[i]) {
+			DPU_ERROR("No more resource %d available to assign to enc %d\n",
+				  type, enc_id);
+			break;
+		}
 		blks[num_blks++] = hw_blks[i];
 	}
 
-- 
2.39.0