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Message-ID: <a67594cf-eb7f-873f-1c11-ccb4317b6bdf@collabora.com>
Date:   Wed, 23 Nov 2022 10:15:25 +0100
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Subject: Re: [PATCH v2] drm/mediatek: Clean dangling pointer on bind error
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        <nfraprado@collabora.com>, Chun-Kuang Hu <chunkuang.hu@kernel.org>
Cc:     kernel@collabora.com, "Nancy . Lin" <nancy.lin@mediatek.com>,
        CK Hu <ck.hu@mediatek.com>,
        Daniel Kurtz <djkurtz@chromium.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@gmail.com>,
        Mao Huang <littlecvr@chromium.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        YT Shen <yt.shen@mediatek.com>,
        dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mediatek@lists.infradead.org
References: <20221122143949.3493104-1-nfraprado@collabora.com>
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
In-Reply-To: <20221122143949.3493104-1-nfraprado@collabora.com>
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Precedence: bulk

Il 22/11/22 15:39, Nícolas F. R. A. Prado ha scritto:
> mtk_drm_bind() can fail, in which case drm_dev_put() is called,
> destroying the drm_device object. However a pointer to it was still
> being held in the private object, and that pointer would be passed along
> to DRM in mtk_drm_sys_prepare() if a suspend were triggered at that
> point, resulting in a panic. Clean the pointer when destroying the
> object in the error path to prevent this from happening.
> 
> Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")
> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
> 
> ---
> 
> Changes in v2:
> - Added Fixes tag
> 
>   drivers/gpu/drm/mediatek/mtk_drm_drv.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> index 39a42dc8fb85..a21ff1b3258c 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> @@ -514,6 +514,7 @@ static int mtk_drm_bind(struct device *dev)
>   err_deinit:
>   	mtk_drm_kms_deinit(drm);
>   err_free:
> +	private->drm = NULL;

Sorry for not noticing that in v1, but I've rechecked this function and, while this
commit does indeed actually solve the described issue, I think it's incomplete.

A few lines before, we have a loop that sets

		private->all_drm_private[i]->drm = drm;

...so here you should do...

	private->drm = NULL;

	while (i--) /* a for loop will also do, your choice */
		private->all_drm_private[i]->drm = NULL;
		
That makes sure that you cleanup *everything* :-)

Cheers,
Angelo