Re: [PATCH 3/3] mac80211: Implement functionality to monitor station's signal stregnth

[Tamizh chelvam <tamizhr@codeaurora.org>]

On 2018-11-09 17:25, Johannes Berg wrote:
> Oh, umm, that patch is still here ...
> 
> I guess we can combine 2 and 3 too.
> 
> 
Sure.

>> +	if (sta->rssi_low && bss_conf->enable_beacon) {
>> +		int last_event =
>> +			sta->last_rssi_event_value;
>> +		int sig = -ewma_signal_read(&sta->rx_stats_avg.signal);
>> +		int low = sta->rssi_low;
>> +		int high = sta->rssi_high;
> 
> This doesn't really support a list, like in patch 2 where you store
> sta_info::rssi_tholds?
> 
rssi_low and rssi_high will have a configured value or zero know ? 
Configured value has been stored in the previous patch.

>> +		if (sig < low &&
>> +		    (last_event == 0 || last_event >= low)) {
>> +			sta->last_rssi_event_value = sig;
>> +			cfg80211_sta_mon_rssi_notify(
>> +				rx->sdata->dev, sta->addr,
>> +				NL80211_CQM_RSSI_THRESHOLD_EVENT_LOW,
>> +				sig, GFP_ATOMIC);
>> +			rssi_cross = true;
>> +		} else if (sig > high &&
>> +			   (last_event == 0 || last_event <= high)) {
>> +			sta->last_rssi_event_value = sig;
>> +			cfg80211_sta_mon_rssi_notify(
>> +				rx->sdata->dev, sta->addr,
>> +				NL80211_CQM_RSSI_THRESHOLD_EVENT_HIGH,
>> +				sig, GFP_ATOMIC);
>> +			rssi_cross = true;
>> +		}
>> +	}
>> +
>> +	if (rssi_cross) {
>> +		ieee80211_update_rssi_config(sta);
>> +		rssi_cross = false;
>> +	}
>> +}
> 
> Ah, but it does, just hard to understand.
> 
> However, this does mean what I suspected on the other patch is true -
> you're calling ieee80211_update_rssi_config() here, and that uses the
> sta->rssi_tholds array without any protection, while a concurrent 
> change
> of configuration can free the data.
> 
yes, I'll add a protection mechanism.

> You need to sort that out. I would suggest to stick all the sta->rssi_*
> fields you add into a new struct (you even had an empty one), and
> protect that struct using RCU. That also saves the memory in case it's
> not assigned at all. Something like
> 
> struct sta_mon_rssi_config {
> 	struct rcu_head rcu_head;
> 	int n_thresholds;
> 	s32 low, high;
> 	u32 hyst;
> 	s32 last_value;
> 	s32 thresholds[];
> };
> 
> then you can kfree_rcu() it, and just do a single allocation using
> struct_size() for however many entries you need.
> 
Yes correct. I'll change it.

>> + * @count_rx_signal: Number of data frames used in averaging station 
>> signal.
>> + *	This can be used to avoid generating less reliable station rssi 
>> cross
>> + *	events that would be based only on couple of received frames.
>>   */
>>  struct sta_info {
>>  	/* General information, mostly static */
>> @@ -600,6 +603,7 @@ struct sta_info {
>>  	s32 rssi_high;
>>  	u32 rssi_hyst;
>>  	s32 last_rssi_event_value;
>> +	unsigned int count_rx_signal;
> 
> I guess that would also move into the new struct.
> 
Okay.

Thanks,
Tamizh.