Lockup in wpa supplicant

Jouni Malinen j at w1.fi
Fri May 30 03:19:35 EDT 2014


On Fri, May 30, 2014 at 10:02:28AM +1000, michaelm wrote:
> I am using wpa_supplicant 2.1 with linux wireless driver
> 
> The problem I am having is that after a while, wpa_supplicant hangs in the function "radio_start_next_work" first giving the message:
> "Delay radio work start until externally triggered scan completes"

My first guess is that this is caused by a bug that was fixed after 2.1:
http://w1.fi/cgit/hostap/commit/?id=1b5df9e591d9e97b69d7b2b69c295a5365f389c9

How easily can you reproduce this issue? The log you included here did
not have enough context to see what happened (the issue had happened
before the start of that excerpt). I would suggest testing with the
current hostap.git master branch snapshot since there has been number of
fixes in to the radio work handling (in addition to that more specific
fix that I mentioned above). If you can reproduce with the current
snapshot, I would be interested in seeing a more complete debug log
showing the issue.

> Without full debugging, it seems that wpa_s->external_scan_running flag is set forever and hence wpa_supplicant never does any radio work.

> I cannot really explain why there should be an externally triggered scan (as it would be the only condition to set the "external_scan_running" flag).

That's not really true. The bug mentioned above resulted in a special
scan case being triggered by wpa_supplicant as being assumed to be
externally triggered.

> I thought this may be to do with the fact that hostapd is running at the same time (as we use both STA and AP functionality simultaneously) but
> this occurs even with AP function disabled and hostapd not running.
> 
> If I remove the return, e.g.:
> 	if (wpa_s && wpa_s->external_scan_running) {
> 	    /*
>             ** log message, but do not return and proceed with radio work
>             */
> 		wpa_printf(MSG_DEBUG, "<<<<Delay radio work start until externally triggered scan completes>>>>");
> 		/* return; */
> 	}
> 
> Everything seems to work fine. Furthermore, it doesn't seem that interrupting external scan if supplicant needs to do its own is such a bad idea.

That's not the proper way to fix this. If there had actually been a real
scan pending, cfg80211 would be blocking any new scan attempts.

-- 
Jouni Malinen                                            PGP id EFC895FA


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