Re: [PATCH] drm/bridge: megachips: Fix error handling in i2c_register_driver()

From: Andrzej Hajda <andrzej.hajda@intel.com>
To: Yuan Can <yuancan@huawei.com>,
	peter.senna@gmail.com, martin.donnelly@ge.com,
	martyn.welch@collabora.co.uk, neil.armstrong@linaro.org,
	robert.foss@linaro.org, Laurent.pinchart@ideasonboard.com,
	jonas@kwiboo.se, jernej.skrabec@gmail.com, airlied@gmail.com,
	daniel@ffwll.ch, architt@codeaurora.org,
	dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/bridge: megachips: Fix error handling in i2c_register_driver()
Date: Tue, 8 Nov 2022 09:50:00 +0100	[thread overview]
Message-ID: <aa5ffd76-d95a-8aea-ddc9-eaf8e95a73ce@intel.com> (raw)
In-Reply-To: <20221108082956.35802-1-yuancan@huawei.com>

On 08.11.2022 09:29, Yuan Can wrote:
> A problem about insmod megachips-stdpxxxx-ge-b850v3-fw.ko failed is
> triggered with the following log given:
>
> [ 4497.981497] Error: Driver 'stdp4028-ge-b850v3-fw' is already registered, aborting...
> insmod: ERROR: could not insert module megachips-stdpxxxx-ge-b850v3-fw.ko: Device or resource busy
>
> The reason is that stdpxxxx_ge_b850v3_init() returns i2c_add_driver()
> directly without checking its return value, if i2c_add_driver() failed,
> it returns without calling i2c_del_driver() on the previous i2c driver,
> resulting the megachips-stdpxxxx-ge-b850v3-fw can never be installed
> later.
> A simple call graph is shown as below:
>
>   stdpxxxx_ge_b850v3_init()
>     i2c_add_driver(&stdp4028_ge_b850v3_fw_driver)
>     i2c_add_driver(&stdp2690_ge_b850v3_fw_driver)
>       i2c_register_driver()
>         driver_register()
>           bus_add_driver()
>             priv = kzalloc(...) # OOM happened
>     # return without delete stdp4028_ge_b850v3_fw_driver
>
> Fix by calling i2c_del_driver() on stdp4028_ge_b850v3_fw_driver when
> i2c_add_driver() returns error.
>
> Fixes: fcfa0ddc18ed ("drm/bridge: Drivers for megachips-stdpxxxx-ge-b850v3-fw (LVDS-DP++)")
> Signed-off-by: Yuan Can <yuancan@huawei.com>
> ---
>   drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> index 97359f807bfc..0d037eeefcf3 100644
> --- a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> +++ b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> @@ -440,7 +440,13 @@ static int __init stdpxxxx_ge_b850v3_init(void)
>   	if (ret)
>   		return ret;
>   
> -	return i2c_add_driver(&stdp2690_ge_b850v3_fw_driver);
> +	ret = i2c_add_driver(&stdp2690_ge_b850v3_fw_driver);
> +	if (ret) {
> +		i2c_del_driver(&stdp4028_ge_b850v3_fw_driver);
> +		return ret;
> +	}
> +
> +	return 0;

Could be:
ret = i2c_add_driver(&stdp2690_ge_b850v3_fw_driver);
if (ret)
     i2c_del_driver(&stdp4028_ge_b850v3_fw_driver);
return ret;

Up to you. Anyway:
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>

Regards
Andrzej

>   }
>   module_init(stdpxxxx_ge_b850v3_init);
>   