linux-kernel - [PATCH 6/7] net/netfilter/nf_conntrack_core: Remove barriers after spin_unlock

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Message-Id: <1472742257-10515-7-git-send-email-manfred@colorfullife.com>
Date:   Thu,  1 Sep 2016 17:04:16 +0200
From:   Manfred Spraul <manfred@...orfullife.com>
To:     benh@...nel.crashing.org, paulmck@...ux.vnet.ibm.com,
        Ingo Molnar <mingo@...e.hu>, Boqun Feng <boqun.feng@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, will.deacon@....com,
        1vier1@....de, Davidlohr Bueso <dave@...olabs.net>,
        Manfred Spraul <manfred@...orfullife.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        netfilter-devel@...r.kernel.org
Subject: [PATCH 6/7] net/netfilter/nf_conntrack_core: Remove barriers after spin_unlock_wait

nf_conntrack_all() contains an smp_rmb() after spin_unlock_wait().
This was done to allow safe backporting.

Commit 2c6100227116 ("locking/qspinlock: Fix spin_unlock_wait() some more")
(and the commits for the other archs) ensure that spin_unlock_wait()
is an ACQUIRE.
Therefore the smp_rmb() after spin_unlock_wait() can be removed.

Not for stable!

Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
Cc: Pablo Neira Ayuso <pablo@...filter.org>
Cc: netfilter-devel@...r.kernel.org
---
 net/netfilter/nf_conntrack_core.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 3847f09..c8a2d26 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -153,11 +153,6 @@ static void nf_conntrack_all_lock(void)
 	for (i = 0; i < CONNTRACK_LOCKS; i++) {
 		spin_unlock_wait(&nf_conntrack_locks[i]);
 	}
-	/* spin_unlock_wait() is at least a control barrier.
-	 * Add smp_rmb() to upgrade it to an ACQUIRE, it must
-	 * pair with the spin_unlock(&nf_conntrack_locks[])
-	 */
-	smp_rmb();
 }
 
 static void nf_conntrack_all_unlock(void)
-- 
2.7.4