From: "Paul E. McKenney" <paulmck@linux•vnet.ibm.com>
To: Eric Dumazet <eric.dumazet@gmail•com>
Cc: linux-kernel@vger•kernel.org, mingo@kernel•org,
laijs@cn•fujitsu.com, dipankar@in•ibm.com,
akpm@linux-foundation•org, mathieu.desnoyers@efficios•com,
josh@joshtriplett•org, niv@us•ibm.com, tglx@linutronix•de,
peterz@infradead•org, rostedt@goodmis•org, dhowells@redhat•com,
edumazet@google•com, darren@dvhart•com, fweisbec@gmail•com,
sbw@mit•edu, "David S. Miller" <davem@davemloft•net>,
Alexey Kuznetsov <kuznet@ms2•inr.ac.ru>,
James Morris <jmorris@namei•org>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6•org>,
Patrick McHardy <kaber@trash•net>,
netdev@vger•kernel.org
Subject: Re: [PATCH v2 tip/core/rcu 07/13] ipv6/ip6_tunnel: Apply rcu_access_pointer() to avoid sparse false positive
Date: Wed, 9 Oct 2013 14:57:47 -0700 [thread overview]
Message-ID: <20131009215747.GA5790@linux.vnet.ibm.com> (raw)
In-Reply-To: <1381354949.4971.20.camel@edumazet-glaptop.roam.corp.google.com>
On Wed, Oct 09, 2013 at 02:42:29PM -0700, Eric Dumazet wrote:
> On Wed, 2013-10-09 at 14:29 -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@linux•vnet.ibm.com>
> >
> > The sparse checking for rcu_assign_pointer() was recently upgraded
> > to reject non-__kernel address spaces. This also rejects __rcu,
> > which is almost always the right thing to do. However, the use in
> > ip6_tnl_unlink() is legitimate: It is assigning a pointer to an element
> > from an RCU-protected list, and all elements of this list are already
> > visible to caller.
> >
> > This commit therefore silences this false positive by laundering the
> > pointer using rcu_access_pointer() as suggested by Josh Triplett.
> >
> > Reported-by: kbuild test robot <fengguang.wu@intel•com>
> > Signed-off-by: Paul E. McKenney <paulmck@linux•vnet.ibm.com>
> > Cc: "David S. Miller" <davem@davemloft•net>
> > Cc: Alexey Kuznetsov <kuznet@ms2•inr.ac.ru>
> > Cc: James Morris <jmorris@namei•org>
> > Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6•org>
> > Cc: Patrick McHardy <kaber@trash•net>
> > Cc: netdev@vger•kernel.org
> > ---
> > net/ipv6/ip6_tunnel.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
> > index 61355f7f4da5..ecc0166e1a9c 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);
> > + rcu_assign_pointer(*tp, rcu_access_pointer(t->next));
> > break;
> > }
> > }
>
> Then it seems a mere "*tp = t->next;" would be enough ?
>
> We do not really need a barrier.
Hmmm... I could use RCU_INIT_POINTER(). Something like the following?
RCU_INIT_POINTER(ACCESS_ONCE(*tp), t->next);
The ACCESS_ONCE() to prevent the compiler from doing anything stupid.
Presumably the value of t->next cannot change, so a normal load suffices.
Or did you have something else in mind?
Thanx, Paul
next prev parent reply other threads:[~2013-10-09 21:57 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-09 21:29 [PATCH v2 tip/core/rcu 0/13] Sparse-related updates for 3.13 Paul E. McKenney
[not found] ` <1381354186-16285-1-git-send-email-paulmck@linux.vnet.ibm.com>
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 03/13] bridge: Apply rcu_access_pointer() to avoid sparse false positive Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 04/13] wireless: " Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 05/13] decnet: " Paul E. McKenney
2013-10-09 22:28 ` Josh Triplett
2013-10-09 22:46 ` Paul E. McKenney
2013-10-09 22:57 ` Josh Triplett
2013-10-09 23:57 ` Paul E. McKenney
2013-10-09 22:58 ` Dhaval Giani
2013-10-09 23:54 ` Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 06/13] ipv4/ip_socketglue: " Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 07/13] ipv6/ip6_tunnel: " Paul E. McKenney
2013-10-09 21:42 ` Eric Dumazet
2013-10-09 21:57 ` Paul E. McKenney [this message]
2013-10-09 22:10 ` Eric Dumazet
2013-10-09 22:36 ` Paul E. McKenney
2013-10-09 22:51 ` Eric Dumazet
2013-10-09 22:56 ` Josh Triplett
2013-10-09 23:17 ` Eric Dumazet
2013-10-09 23:40 ` Josh Triplett
2013-10-10 0:12 ` Eric Dumazet
2013-10-10 0:28 ` Paul E. McKenney
2013-10-10 2:04 ` Hannes Frederic Sowa
2013-10-10 19:05 ` Paul E. McKenney
2013-10-12 2:25 ` Hannes Frederic Sowa
2013-10-12 7:53 ` Paul E. McKenney
2013-10-12 16:43 ` Hannes Frederic Sowa
2013-10-12 17:37 ` Hannes Frederic Sowa
2013-10-12 19:42 ` Mathieu Desnoyers
2013-10-13 11:14 ` Paul E. McKenney
2013-10-13 20:11 ` Hannes Frederic Sowa
2013-10-11 0:20 ` Josh Triplett
2013-10-11 13:25 ` Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 08/13] ipv6/ip6_gre: " Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 09/13] ipv6/sit: " Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 10/13] mac80211: " Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 11/13] bridge/br_mdb: " Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 12/13] bonding/bond_main: " Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 13/13] bonding/bond_alb.c: " Paul E. McKenney
2013-10-09 22:18 ` [PATCH v2 tip/core/rcu 0/13] Sparse-related updates for 3.13 Josh Triplett
2013-10-09 22:46 ` Paul E. McKenney
2013-10-09 22:23 ` Josh Triplett
2013-10-09 22:30 ` Josh Triplett
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