[PATCH] Do not retry scan after failure if operating in ap_mode

Pasi Sjöholm pasi.sjoholm at jolla.com
Mon Aug 10 07:53:10 EDT 2015

On 08.08.2015 23:17, Jouni Malinen wrote:
> On Wed, Aug 05, 2015 at 01:42:35AM +0300, pasi.sjoholm at jolla.com
> wrote:
>> Commit 2d9c99e37b29a639dafa431df38e1586a31ba887 introduced a
>> regression while running in ap_mode together with ap_scan 
>> configured with value of 2.
>> Retrying caused following path to be called: 
>> wpa_supplicant_req_scan()->wpa_supplicant_scan()-> 
>> wpa_supplicant_assoc_try()->wpa_supplicant_associate()-> 
>> wpa_supplicant_create_ap()
>> Which eventually teared down the currently configured ap_mode by
>> calling wpa_supplicant_ap_deinit().
> Would you be able to provide a debug log showing the sequence in
> which this is hit?

Yes, I can provide it. Will try to send it later today.

>> @@ -186,6 +186,9 @@ static void wpas_trigger_scan_cb(struct
>> wpa_radio_work *work, int deinit) if (wpa_s->disconnected) retry
>> = 0;
>> +		if (wpa_s->last_ssid && wpa_s->last_ssid->mode ==
>> WPAS_MODE_AP) +			retry = 0;
> This would imply that we are currently running an AP mode interface
> and something start a scan. What was that something? And what
> happened next? I'm trying to understand especially that
> wpa_supplicant_assoc_try() call in the sequence. Why would that be
> called here when AP mode was already running?

This is happening due external process requesting for a scan over dbus
which then triggers wpa_supplicant_trigger_scan().

Eg. Let's have mobile device running in AP mode and user starting an
application which wants show/use the device location by using
available wlan networks as one the of inputs in addition to cellular
network cells.

Anyway, the device wlan chip does not support scanning (errno:
operation not supported) while it's running in AP mode and therefore
wpa_supplicant retries the scanning after initial scan failed.

Eventually in wpa_supplicant_scan() there's a code section:

        if (wpa_s->last_scan_req != MANUAL_SCAN_REQ &&
            wpa_s->conf->ap_scan == 2) {
                wpa_s->connect_without_scan = NULL;
                wpa_s->prev_scan_wildcard = 0;
                wpa_supplicant_assoc_try(wpa_s, ssid);

The last_scan_req in this case is INITIAL_SCAN_REQ as no scans have
been made after AP mode has been setup, and then we have set ap_scan
with the value of 2.


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