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From: Johannes Berg <johannes@sipsolutions.net>
To: Arik Nemtsov <arik@wizery.com>
Cc: linux-wireless@vger.kernel.org, Luciano Coelho <coelho@ti.com>,
	Jouni Malinen <j@w1.fi>
Subject: Re: [PATCH 02/10] wl12xx: AP-mode - fix race condition on sta connection
Date: Wed, 26 Jan 2011 23:08:39 +0100	[thread overview]
Message-ID: <1296079719.3635.47.camel@jlt3.sipsolutions.net> (raw)
In-Reply-To: <AANLkTikno8Aa3wKy1js62D3FLOZJUxPyuwYsQd+g8JBM@mail.gmail.com>

On Thu, 2011-01-27 at 00:02 +0200, Arik Nemtsov wrote:

> >> 2. The STA transmits something
> >> 3. The AP FW deauths the STA
> >> 4. hostapd adds the station, causing mac80211 to call add_sta(), which
> >> causes the FW to add the sta
> >>
> >> Then we have an endless loop of sta add/remove..
> >
> > I'd wondered about that race condition before -- maybe hostapd should
> > add the station before sending the assoc complete. The race also exists
> > in practice with just mac80211, except it only leads to a dropped frame.
> 
> Well it can still get dropped here. This just prevents the FW from
> de-authenticating the STA.

No I mean the incoming frame would be dropped:

 - sta sends assoc
 - hostapd sends response
 - when assoc response ACK is received, hostapd sets state to assoc
 - incoming frame
 - hostapd adds STA to mac80211

then in this case mac80211 will pass the incoming frame up to hostapd,
and not to the network stack, but hostapd knows that it's a good frame
and won't kick out the station

The only difference is that with your firmware the kicking out is done
by the firmware, not hostapd, so it actually gets kicked out rather than
the frame being dropped.

So ... the race exists even without the firmware, it just has less
severe consequences.

If we add the station before the response frame's ACK is received, we
still have the race, and we need to delete if we don't get the ACK. If
we add the station before we send the assoc response we get rid of this
race, but also have to delete if we don't get the ACK. I guess that case
is actually nicer in some way since we would have allowed the station to
connect, so if spurious data frames go up because we don't get an ACK
from the station that's no big deal?

johannes


  reply	other threads:[~2011-01-26 22:08 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-16  5:42 [PATCH 00/10] wl12xx: AP-mode per link PSM Arik Nemtsov
2011-01-16  5:42 ` [PATCH 01/10] wl12xx: fix potential race condition with TX queue watermark Arik Nemtsov
2011-01-16  5:42 ` [PATCH 02/10] wl12xx: AP-mode - fix race condition on sta connection Arik Nemtsov
2011-01-26 14:01   ` Luciano Coelho
2011-01-26 20:04     ` Arik Nemtsov
2011-01-26 21:28       ` Luciano Coelho
2011-01-26 21:33   ` Johannes Berg
2011-01-26 21:44     ` Arik Nemtsov
2011-01-26 21:54       ` Johannes Berg
2011-01-26 22:02         ` Arik Nemtsov
2011-01-26 22:08           ` Johannes Berg [this message]
2011-01-26 22:16             ` Arik Nemtsov
2011-01-26 23:11               ` Johannes Berg
2011-01-27  0:20             ` Jouni Malinen
2011-01-27  8:21               ` Johannes Berg
2011-01-16  5:42 ` [PATCH 03/10] wl12xx: AP-mode - TX queue per link in AC Arik Nemtsov
2011-01-16  5:42 ` [PATCH 04/10] mac80211: do not calc frame duration when using HW rate-control Arik Nemtsov
2011-01-16  8:34   ` Johannes Berg
2011-01-16  5:42 ` [PATCH 05/10] wl12xx: report invalid TX rate when returning non-TX-ed skbs Arik Nemtsov
2011-01-27  9:51   ` Luciano Coelho
2011-01-27 10:33     ` Johannes Berg
2011-01-30  6:57       ` Arik Nemtsov
2011-01-16  5:42 ` [PATCH 06/10] mac80211: add HW flag for disabling auto link-PS in AP mode Arik Nemtsov
2011-01-16  8:50   ` Johannes Berg
     [not found]     ` <AANLkTik=WDsehr0EgW7QemfdmokvaLzg1ugASwiuCOXt@mail.gmail.com>
2011-01-16 21:53       ` Fwd: " Arik Nemtsov
2011-01-17  9:35         ` Johannes Berg
2011-01-17 22:47           ` Arik Nemtsov
2011-01-18  9:05             ` Johannes Berg
2011-01-18 19:17               ` Arik Nemtsov
2011-01-27 11:39   ` Luciano Coelho
2011-01-16  5:42 ` [PATCH 07/10] wl12xx: AP-mode - support HW based link PS monitoring Arik Nemtsov
2011-01-27 11:41   ` Luciano Coelho
2011-01-16  5:42 ` [PATCH 08/10] wl12xx: AP mode - fix bug in cleanup of wl1271_op_sta_add() Arik Nemtsov
2011-01-16  5:42 ` [PATCH 09/10] wl12xx: AP-mode - count free FW TX blocks per link Arik Nemtsov
2011-01-16  5:42 ` [PATCH 10/10] wl12xx: AP-mode - management of links in PS-mode Arik Nemtsov

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