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Date: Fri, 17 Jul 2015 08:54:25 +1000 From: Benjamin Herrenschmidt <benh@...nel.crashing.org> To: paulmck@...ux.vnet.ibm.com Cc: Michael Ellerman <mpe@...erman.id.au>, Will Deacon <will.deacon@....com>, "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org> Subject: Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() On Thu, 2015-07-16 at 08:11 -0700, Paul E. McKenney wrote: > > So isync in lock in architecturally incorrect, despite being what > the > > architecture recommends using, yay ! > > Well, the architecture isn't expecting that crazies like myself would > want to have an unlock-lock provide ordering to some CPU not holding > the lock. :-/ Yes, isync in lock effectively allows any load or store before the lock to leak into the lock and get re-ordered with things in there. lwsync leaves us exposed to the re-order inside the LL/SC of a subsequent load. So to get the full barrier semantic, the only option is a full sync, either in lock or unlock. Instinctively I prefer in lock but there's an argument to have it in unlock so we can get rid of the iosync business. Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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