Subject: Re: [PATCH 00/18] mac80211 cleanups and fixes
From: Johannes Berg <johannes@sipsolutions.net>
To: "Luis R. Rodriguez" <lrodriguez@atheros.com>
Cc: Sujith Manoharan <Sujith.Manoharan@Atheros.com>,
	John Linville <linville@tuxdriver.com>,
	"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
In-Reply-To: <20080911165011.GA6049@tesla>
References: <20080910220145.707263000@sipsolutions.net>
	 <18632.55008.411078.289830@gargle.gargle.HOWL>
	 <1221139351.6986.26.camel@johannes.berg>  <20080911165011.GA6049@tesla>
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Date: Thu, 11 Sep 2008 18:53:15 +0200
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On Thu, 2008-09-11 at 09:50 -0700, Luis R. Rodriguez wrote:

> > I had actually tried
> > (http://johannes.sipsolutions.net/patches/kernel/ath9k-sta-node.patch)
> > but you're using refcounting for the nodes while mac80211 RCU-protects
> > them, so I didn't get very far.
>=20
> Good thing I read RCU docs yesterday.

Heh.

> We should be able to remove ref counts and simply use RCU and
> sychronize_rcu() before deletion.

Well you don't get to control deletion then, that's another thing.

> > It needs a bit more effort to make sure
> > you don't have node pointers stick around in some tx descriptor after
> > mac80211 decides to remove a node (which may very well happen while
> > frames are queued)
>=20
> We can call_rcu() here no, and let the driver deal with what it needs to
> prior to deletion?

The driver already gets notified via sta_notify() that the sta is about
to be deleted, it must make sure that no matter what sort of references
it kept, the sta will not be accessed after that sta_notify call.

johannes

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