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Date: Tue, 04 Jan 2011 15:09:15 +0600
From: Eugene Grosbein <egrosbein@rdtc.ru>
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Cc: freebsd-net@freebsd.org, bug-followup@freebsd.org
Subject: Re: kern/153594: [iwn] Network keeps disconnecting when
 /etc/rc.d/netif restart is run
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On 04.01.2011 15:06, Bernhard Schmidt wrote:

>> Perhaps, wrapping wpa_supplicant invocation into "lockf -t0" would help
>> to eliminate race?
> 
> Possibly, but I don't think this is the way to go.
> 
> Currently wpa_supplicant has this code:
>         /*
>          * Mark the interface as down to ensure wpa_supplicant has exclusive
>          * access to the net80211 state machine, do this before opening the
>          * route socket to avoid a false event that the interface disappeared.
>          */
>         if (getifflags(drv, &flags) == 0)
>                 (void) setifflags(drv, flags &~ IFF_UP);
> 
> This code works such that it will send an event to already running 
> wpa_supplicant instances which will then terminate. This does indeed work if 
> there's enough delay between invocations, though, if there is just a small 
> delay (~100ms or something), that event doesn't get passed probably. I think 
> we should start looking into possible solution at that point, trying to figure 
> out why the the event doesn't get passed (probably because the interface is 
> not yet up at that point) will get us closer to proper solution.

Proper fine-grained locking was always good solution for race problem :-)
How about using flock(2) in wpa_supplicant source code?

Eugene Grosbein