From: Yogesh Powar <yogeshp@marvell.com>
To: Johannes Berg <johannes@sipsolutions.net>
CC: "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	"John W. Linville" <linville@tuxdriver.com>,
	Andreas Hartmann <andihartmann@01019freenet.de>
Date: Thu, 23 Jun 2011 04:52:39 -0700
Subject: RE: [PATCH 2/2] mac80211: Fixing Races for skipping tailroom
 reservation
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>What I'm worried about is that there's no memory barrier after the
>counter update, so how do we know it cannot happen after
>synchronize_rcu()? I think we need something like rcu_assign_pointer()
>but I don't see rcu_assign_index() (any more?)

I did not find much on rcu_assign_index other than
http://markmail.org/thread/h53fuecyo5odg6xv which has this function defined as

+#define rcu_assign_index(p, v) ({ \
+               smp_wmb(); \
+               (p) = (v); \
+        })      

Will smp_wmb() do the trick?
counter++;
smp_wmb();
synchronize_rcu();

or will have to move to pointer logic? And use rcu_assign_pointer at key.c and
rcu_dereference at tx.c with overhead of kmalloc and kfree?

Thanks
Yogesh