Re: [PATCH net-next-2.6] net: inet_add_protocol() can use cmpxchg()

[Eric Dumazet <eric.dumazet@gmail.com>]

Le jeudi 09 septembre 2010 à 09:08 +0000, Jarek Poplawski a écrit :
> 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.

Jarek, cmpxchg() is a very strong primitive, as documented
in Documentation/memory-barriers.txt :

<begin of quote>

Any atomic operation that modifies some state in memory and returns information
about the state (old or new) implies an SMP-conditional general memory barrier
(smp_mb()) on each side of the actual operation (with the exception of
explicit lock operations, described later).  These include:

        xchg();
        cmpxchg();
...
These are used for such things as implementing LOCK-class and UNLOCK-class
operations and adjusting reference counters towards object destruction, and as
such the implicit memory barrier effects are necessary.

<end of quote>

Its not needed to document each cmpxchg() use, because of these
strong requirements.