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Message-ID: <20151007111915.GF17308@twins.programming.kicks-ass.net> Date: Wed, 7 Oct 2015 13:19:15 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Will Deacon <will.deacon@....com> Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: Re: [PATCH v2] barriers: introduce smp_mb__release_acquire and update documentation On Wed, Oct 07, 2015 at 11:59:28AM +0100, Will Deacon wrote: > As much as we'd like to live in a world where RELEASE -> ACQUIRE is > always cheaply ordered and can be used to construct UNLOCK -> LOCK > definitions with similar guarantees, the grim reality is that this isn't > even possible on x86 (thanks to Paul for bringing us crashing down to > Earth). > > This patch handles the issue by introducing a new barrier macro, > smp_mb__release_acquire, that can be placed between a RELEASE and a > subsequent ACQUIRE operation in order to upgrade them to a full memory > barrier. At the moment, it doesn't have any users, so its existence > serves mainly as a documentation aid. Does we want to go revert 12d560f4ea87 ("rcu,locking: Privatize smp_mb__after_unlock_lock()") for that same reason? > Documentation/memory-barriers.txt is updated to describe more clearly > the ACQUIRE and RELEASE ordering in this area and to show an example of > the new barrier in action. The only nit I have is that if we revert the above it might be make sense to more clearly call out the distinction between the two. -- 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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