linux-kernel - Re: [PATCH v1 2/3] media: cedrus: Set the platform driver data earlier

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Date:   Mon, 22 Aug 2022 22:57:39 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Jernej Škrabec <jernej.skrabec@...il.com>,
        linux-media@...r.kernel.org, Maxime Ripard <mripard@...nel.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>
Cc:     kernel@...labora.com,
        Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        stable@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/3] media: cedrus: Set the platform driver data
 earlier

On 8/20/22 3:25 AM, Jernej Škrabec wrote:
> Dne petek, 19. avgust 2022 ob 17:37:20 CEST je Nicolas Dufresne napisal(a):
>> Le vendredi 19 août 2022 à 06:17 +0200, Jernej Škrabec a écrit :
>>> Dne četrtek, 18. avgust 2022 ob 22:33:07 CEST je Nicolas Dufresne 
> napisal(a):
>>>> From: Dmitry Osipenko <dmitry.osipenko@...labora.com>
>>>>
>>>> The cedrus_hw_resume() crashes with NULL deference on driver probe if
>>>> runtime PM is disabled because it uses platform data that hasn't been
>>>> set up yet. Fix this by setting the platform data earlier during probe.
>>>
>>> Does it even work without PM? Maybe it would be better if Cedrus would
>>> select PM in Kconfig.
>>
>> I cannot comment myself on this, but it does not seem to invalidate this
>> Dmitry's fix.
> 
> If NULL pointer dereference happens only when PM is disabled, then it does. I 
> have PM always enabled and I never experienced above issue.

There's still a bug even with PM enabled: the v4l2 device is exposed to
userspace, and therefore userspace could trigger a PM resume, before
platform_set_drvdata() is called.

>>>> Cc: stable@...r.kernel.org
>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
>>>> Signed-off-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>

Please add a Fixes tag. With that:

Reviewed-by: Samuel Holland <samuel@...lland.org>

>>>> ---
>>>>
>>>>  drivers/staging/media/sunxi/cedrus/cedrus.c | 4 ++--
>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c
>>>> b/drivers/staging/media/sunxi/cedrus/cedrus.c index
>>>> 960a0130cd620..55c54dfdc585c 100644
>>>> --- a/drivers/staging/media/sunxi/cedrus/cedrus.c
>>>> +++ b/drivers/staging/media/sunxi/cedrus/cedrus.c
>>>> @@ -448,6 +448,8 @@ static int cedrus_probe(struct platform_device
>>>> *pdev)
>>>>
>>>>  	if (!dev)
>>>>  		return -ENOMEM;
>>>>
>>>> +	platform_set_drvdata(pdev, dev);
>>>> +
>>>>  	dev->vfd = cedrus_video_device;
>>>>  	dev->dev = &pdev->dev;
>>>>  	dev->pdev = pdev;
>>>>
>>>> @@ -521,8 +523,6 @@ static int cedrus_probe(struct platform_device
>>>> *pdev)
>>>>
>>>>  		goto err_m2m_mc;
>>>>  	}
>>>>
>>>> -	platform_set_drvdata(pdev, dev);
>>>> -
>>>>  	return 0;
>>>>  
>>>>  err_m2m_mc: