linux-kernel - Re: [PATCH v2 tip/core/rcu 07/13] ipv6/ip6_tunnel: Apply rcu_access

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Message-ID: <1381359077.4971.37.camel@edumazet-glaptop.roam.corp.google.com>
Date:	Wed, 09 Oct 2013 15:51:17 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, "David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 tip/core/rcu 07/13] ipv6/ip6_tunnel: Apply
 rcu_access_pointer() to avoid sparse false positive

On Wed, 2013-10-09 at 15:36 -0700, Paul E. McKenney wrote:

> That would work, though it would probably give sparse complaints.

No sparse error here, as I said types are correct and SPARSE_RCU ready :

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 583b77e..28f8495 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -245,7 +245,7 @@ ip6_tnl_unlink(struct ip6_tnl_net *ip6n, struct ip6_tnl *t)
             (iter = rtnl_dereference(*tp)) != NULL;
             tp = &iter->next) {
                if (t == iter) {
-                       rcu_assign_pointer(*tp, t->next);
+                       ACCESS_ONCE(*tp) = t->next;
                        break;
                }
        }

root@...mazet-glaptop:/usr/src/net-next# grep CONFIG_SPARSE_RCU_POINTER .config
CONFIG_SPARSE_RCU_POINTER=y

root@...mazet-glaptop:/usr/src/net-next# make C=2 net/ipv6/ip6_tunnel.o
make[1]: Nothing to be done for `all'.
make[1]: Nothing to be done for `relocs'.
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CALL    scripts/checksyscalls.sh
  CHECK   scripts/mod/empty.c
  CHECK   net/ipv6/ip6_tunnel.c


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