Re: [PATCH v2] drm/bridge: megachips: Fix error handling in i2c_register_driver()

[Ian Ray <ian.ray@ge.com>]

On Tue, Nov 08, 2022 at 09:12:26AM +0000, 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.
> 

Thank you!

> Fixes: fcfa0ddc18ed ("drm/bridge: Drivers for megachips-stdpxxxx-ge-b850v3-fw (LVDS-DP++)")
> Signed-off-by: Yuan Can <yuancan@huawei.com>
> Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>

Tested-by: Ian Ray <ian.ray@ge.com>

> ---
> Changes in v2:
> - Add Andrzej's Reviewed-by
> - Change to the new error return style suggested by Andrzej
> 
>  drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c | 6 +++++-
>  1 file changed, 5 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..cbfa05a6767b 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 +440,11 @@ 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;
>  }
>  module_init(stdpxxxx_ge_b850v3_init);
>  
> -- 
> 2.17.1
>