Re: A patch to test_power module

[Anton Vorontsov]

On Sun, Jan 27, 2013 at 10:45:43PM +0200, Andrey Gelman wrote:
>     Hello !
>     This patch fixes 2 issues in test_power module:
>     1. the mapping of ac_online parameter to its string value "on / off"
>     was swapped.
>     2. more important ...
>     You could not insmod test_power with module parameters, without
>     causing kernel crash.
>     The reason is that in test_power, setting module parameter value has
>     side effect - power_supply_changed event.
>     As the module parameters are processed prior to calling module_init,
>     power_supply_changed event is generated on behalf module that is not
>     yet initialized, causing some NULL pointer dereference.
>     
>     My solution is to test whether the module has been initialized,
>     prior to calling power_supply_changed.

Hi!

The patch looks good, but it is missing Signed-off-by tag. Plus, you
should also Cc: linux-kernel@xxxxxxxxxxxxxxx on submissions (I've added it
now).

Plus, please don't use html in emails. :)

Thanks a lot!

Anton

> From ccd5b3e916477a3c2a51bbf10a3be8e01f3c85e4 Mon Sep 17 00:00:00 2001
> From: Andrey Gelman <andreyg@xxxxxxxxxxxxxx>
> Date: Sun, 27 Jan 2013 22:16:33 +0200
> Subject: [PATCH] test_power: fix a bug in setting module parameter values
> 
> When the kernel loads a module, module params are processed
> prior to calling module_init. As a result, setting module param
> value should not have side effects, at least as long as the
> module has not been initialized.
> ---
>  drivers/power/test_power.c |   31 +++++++++++++++++++++----------
>  1 file changed, 21 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/power/test_power.c b/drivers/power/test_power.c
> index b99a452..753a74f 100644
> --- a/drivers/power/test_power.c
> +++ b/drivers/power/test_power.c
> @@ -30,6 +30,8 @@ static int battery_technology		= POWER_SUPPLY_TECHNOLOGY_LION;
>  static int battery_capacity		= 50;
>  static int battery_voltage		= 3300;
>  
> +static bool module_initialized	= false;
> +
>  static int test_power_get_ac_property(struct power_supply *psy,
>  				      enum power_supply_property psp,
>  				      union power_supply_propval *val)
> @@ -185,6 +187,7 @@ static int __init test_power_init(void)
>  		}
>  	}
>  
> +	module_initialized = true;
>  	return 0;
>  failed:
>  	while (--i >= 0)
> @@ -209,6 +212,8 @@ static void __exit test_power_exit(void)
>  
>  	for (i = 0; i < ARRAY_SIZE(test_power_supplies); i++)
>  		power_supply_unregister(&test_power_supplies[i]);
> +
> +	module_initialized = false;
>  }
>  module_exit(test_power_exit);
>  
> @@ -221,8 +226,8 @@ struct battery_property_map {
>  };
>  
>  static struct battery_property_map map_ac_online[] = {
> -	{ 0,  "on"  },
> -	{ 1,  "off" },
> +	{ 0,  "off"  },
> +	{ 1,  "on" },
>  	{ -1, NULL  },
>  };
>  
> @@ -295,10 +300,16 @@ static const char *map_get_key(struct battery_property_map *map, int value,
>  	return def_key;
>  }
>  
> +static inline void signal_power_supply_changed(struct power_supply *psy)
> +{
> +	if (module_initialized)
> +		power_supply_changed(psy);
> +}
> +
>  static int param_set_ac_online(const char *key, const struct kernel_param *kp)
>  {
>  	ac_online = map_get_value(map_ac_online, key, ac_online);
> -	power_supply_changed(&test_power_supplies[0]);
> +	signal_power_supply_changed(&test_power_supplies[0]);
>  	return 0;
>  }
>  
> @@ -311,7 +322,7 @@ static int param_get_ac_online(char *buffer, const struct kernel_param *kp)
>  static int param_set_usb_online(const char *key, const struct kernel_param *kp)
>  {
>  	usb_online = map_get_value(map_ac_online, key, usb_online);
> -	power_supply_changed(&test_power_supplies[2]);
> +	signal_power_supply_changed(&test_power_supplies[2]);
>  	return 0;
>  }
>  
> @@ -325,7 +336,7 @@ static int param_set_battery_status(const char *key,
>  					const struct kernel_param *kp)
>  {
>  	battery_status = map_get_value(map_status, key, battery_status);
> -	power_supply_changed(&test_power_supplies[1]);
> +	signal_power_supply_changed(&test_power_supplies[1]);
>  	return 0;
>  }
>  
> @@ -339,7 +350,7 @@ static int param_set_battery_health(const char *key,
>  					const struct kernel_param *kp)
>  {
>  	battery_health = map_get_value(map_health, key, battery_health);
> -	power_supply_changed(&test_power_supplies[1]);
> +	signal_power_supply_changed(&test_power_supplies[1]);
>  	return 0;
>  }
>  
> @@ -353,7 +364,7 @@ static int param_set_battery_present(const char *key,
>  					const struct kernel_param *kp)
>  {
>  	battery_present = map_get_value(map_present, key, battery_present);
> -	power_supply_changed(&test_power_supplies[0]);
> +	signal_power_supply_changed(&test_power_supplies[0]);
>  	return 0;
>  }
>  
> @@ -369,7 +380,7 @@ static int param_set_battery_technology(const char *key,
>  {
>  	battery_technology = map_get_value(map_technology, key,
>  						battery_technology);
> -	power_supply_changed(&test_power_supplies[1]);
> +	signal_power_supply_changed(&test_power_supplies[1]);
>  	return 0;
>  }
>  
> @@ -390,7 +401,7 @@ static int param_set_battery_capacity(const char *key,
>  		return -EINVAL;
>  
>  	battery_capacity = tmp;
> -	power_supply_changed(&test_power_supplies[1]);
> +	signal_power_supply_changed(&test_power_supplies[1]);
>  	return 0;
>  }
>  
> @@ -405,7 +416,7 @@ static int param_set_battery_voltage(const char *key,
>  		return -EINVAL;
>  
>  	battery_voltage = tmp;
> -	power_supply_changed(&test_power_supplies[1]);
> +	signal_power_supply_changed(&test_power_supplies[1]);
>  	return 0;
>  }
>  
> -- 
> 1.7.9.5
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