Subject: Re: mac80211: holding sta_info for non associated stations
From: Johannes Berg <johannes@sipsolutions.net>
To: Tomas Winkler <tomasw@gmail.com>
Cc: Ron Rindjunsky <ron.rindjunsky@intel.com>,
	"John W. Linville" <linville@tuxdriver.com>,
	linux-wireless <linux-wireless@vger.kernel.org>
In-Reply-To: <1ba2fa240804011419l1b825c7cnd02790257af9112c@mail.gmail.com> (sfid-20080401_221920_584454_405C87BE)
References: <c85cb4470803310746h36b20d0egce98f8cea3becb0b@mail.gmail.com>
	 <1207052896.5143.76.camel@johannes.berg>
	 <1ba2fa240804011419l1b825c7cnd02790257af9112c@mail.gmail.com>
	 (sfid-20080401_221920_584454_405C87BE)
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Date: Wed, 02 Apr 2008 11:08:51 +0200
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> >  > If i associate to a random AP "x" (what happened automatically as i
> >  > was configured by ifup scripts to do that), and then scan and
> >  > associate to my desired AP "y", i notice that AP "x" was not removed
> >  > from the mac80211 station table. Then, what happened was that during
> >  > ieee80211_stop, when we reach
> >  >
> >  > list_for_each_entry_rcu(sta, &local->sta_list, list) {
> >  >     if (sta->sdata =3D=3D sdata)
> >  >     ieee80211_sta_tear_down_BA_sessions(dev, sta->addr);
> >  > }
> >  >
> >  > we try to tear down sessions to irrelevant stations (AP "x" in my
> >  > example), which leads to bugs.
> >
> >  Why would that lead to bugs? That station was known, and there are no
> >  sessions for that AP.
>=20
> It's like freeing twice the same a pointer. On what level will you
> check that there are no BA session with this ghost  AP?

I don't see the problem. BA sessions are per-STA-info, so what's the
problem with having a STA-info linger around a bit longer maybe?

> >  There might be a problem in that we forget to remove that AP under som=
e
> >  circumstances but it shouldn't matter, we always can have multiple
> >  stations in our table.
>=20
> Not in STA mode, should be associated only to one AP at a time. (Hope
> this also cover roaming).

True, but BA sessions ought to also work in AP mode and I don't see
where the code differs.

Maybe I misunderstood the problem?

johannes

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