From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: Manfred Spraul <manfred@colorfullife.com>,
benh@kernel.crashing.org, paulmck@linux.vnet.ibm.com,
Ingo Molnar <mingo@elte.hu>, Boqun Feng <boqun.feng@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
1vier1@web.de, Davidlohr Bueso <dave@stgolabs.net>,
Pablo Neira Ayuso <pablo@netfilter.org>,
netfilter-devel@vger.kernel.org
Subject: Re: [PATCH 8/7] net/netfilter/nf_conntrack_core: Remove another memory barrier
Date: Thu, 1 Sep 2016 18:41:26 +0200 [thread overview]
Message-ID: <20160901164126.GZ10153@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160901153039.GN6721@arm.com>
On Thu, Sep 01, 2016 at 04:30:39PM +0100, Will Deacon wrote:
> On Thu, Sep 01, 2016 at 05:27:52PM +0200, Manfred Spraul wrote:
> > Since spin_unlock_wait() is defined as equivalent to spin_lock();
> > spin_unlock(), the memory barrier before spin_unlock_wait() is
> > also not required.
Note that ACQUIRE+RELEASE isn't a barrier.
Both are semi-permeable and things can cross in the middle, like:
x = 1;
LOCK
UNLOCK
r = y;
can (validly) get re-ordered like:
LOCK
r = y;
x = 1;
UNLOCK
So if you want things ordered, as I think you do, I think the smp_mb()
is still needed.
RELEASE + ACQUIRE otoh, that is a load-store barrier (but not
transitive).
next prev parent reply other threads:[~2016-09-01 16:41 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-01 15:27 [PATCH 8/7] net/netfilter/nf_conntrack_core: Remove another memory barrier Manfred Spraul
2016-09-01 15:27 ` [PATCH 9/7] ipc/sem.c: " Manfred Spraul
2016-09-01 15:30 ` [PATCH 8/7] net/netfilter/nf_conntrack_core: " Will Deacon
2016-09-01 16:41 ` Peter Zijlstra [this message]
2016-09-02 6:17 ` Boqun Feng
2016-09-02 6:35 ` Manfred Spraul
2016-09-02 19:22 ` Peter Zijlstra
2016-09-03 5:33 ` Manfred Spraul
2016-09-05 18:57 ` Manfred Spraul
2016-09-06 17:56 ` Will Deacon
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