From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jarek Poplawski <jarkao2@gmail.com>
Subject: Re: [PATCH net-next-2.6] net: inet_add_protocol() can use cmpxchg()
Date: Thu, 9 Sep 2010 09:42:11 +0000
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Cc: David Miller <davem@davemloft.net>, jesse@nicira.com,
	netdev@vger.kernel.org
To: Eric Dumazet <eric.dumazet@gmail.com>
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On Thu, Sep 09, 2010 at 11:23:57AM +0200, Eric Dumazet wrote:
> Le jeudi 09 septembre 2010 ?? 09:08 +0000, Jarek Poplawski a =E9crit =
:
> > xactly, without "after some time" I couldn't tell this
> > either. Is seems some barriers might have been changed, but I might
> > be wrong. Anyway, it would be nice to have some comment on that in
> > the changelog.
>=20
> Jarek, cmpxchg() is a very strong primitive, as documented
> in Documentation/memory-barriers.txt :
>=20
> <begin of quote>
>=20
> Any atomic operation that modifies some state in memory and returns i=
nformation
> about the state (old or new) implies an SMP-conditional general memor=
y barrier
> (smp_mb()) on each side of the actual operation (with the exception o=
f
> explicit lock operations, described later).  These include:
>=20
>         xchg();
>         cmpxchg();
> ...
> These are used for such things as implementing LOCK-class and UNLOCK-=
class
> operations and adjusting reference counters towards object destructio=
n, and as
> such the implicit memory barrier effects are necessary.
>=20
> <end of quote>
>=20
> Its not needed to document each cmpxchg() use, because of these
> strong requirements.

OK! I should remember this until "after some time". ;-)

Thanks for the explanation,
Jarek P.