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Message-ID: <20100909094211.GA8404@ff.dom.local> Date: Thu, 9 Sep 2010 09:42:11 +0000 From: Jarek Poplawski <jarkao2@...il.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: David Miller <davem@...emloft.net>, jesse@...ira.com, netdev@...r.kernel.org Subject: Re: [PATCH net-next-2.6] net: inet_add_protocol() can use cmpxchg() On Thu, Sep 09, 2010 at 11:23:57AM +0200, Eric Dumazet wrote: > Le jeudi 09 septembre 2010 ?? 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. OK! I should remember this until "after some time". ;-) Thanks for the explanation, Jarek P. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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