From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
linux-kernel@vger.kernel.org, mingo@kernel.org,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
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: Fri, 11 Oct 2013 06:25:12 -0700 [thread overview]
Message-ID: <20131011132512.GW5790@linux.vnet.ibm.com> (raw)
In-Reply-To: <20131011002044.GA32546@jtriplet-mobl1>
On Thu, Oct 10, 2013 at 05:20:44PM -0700, Josh Triplett wrote:
> On Wed, Oct 09, 2013 at 05:28:33PM -0700, Paul E. McKenney wrote:
> > On Wed, Oct 09, 2013 at 05:12:40PM -0700, Eric Dumazet wrote:
> > > On Wed, 2013-10-09 at 16:40 -0700, Josh Triplett wrote:
> > >
> > > > that. Constructs like list_del_rcu are much clearer, and not
> > > > open-coded. Open-coding synchronization code is almost always a Bad
> > > > Idea.
> > >
> > > OK, so you think there is synchronization code.
> > >
> > > I will shut up then, no need to waste time.
> >
> > As you said earlier, we should at least get rid of the memory barrier
> > as long as we are changing the code.
> >
> > Josh, what would you suggest as the best way to avoid the memory barrier,
> > keep sparse happy, and not be too ugly?
>
> The more I think about it, the more I realize that assigning an __rcu
> pointer to an __rcu pointer *without* a memory barrier is a sufficiently
> uncommon case that you probably *should* just write an open-coded
> assignment. Just please put a very clear comment right before it.
Fair enough, will do! Given earlier email, I believe that Eric is
fine with this, and if he isn't I am sure he will let us know. ;-)
> I'd originally thought it might make sense to have a macro similar to
> rcu_assign_pointer, but I just don't think this is a common enough case,
> and we don't want people thinking they can use this in general for __rcu
> to __rcu assignments (most of which still need a memory barrier).
Yep, it is a rather small fraction of rcu_assign_pointer() instances.
Thanx, Paul
next prev parent reply other threads:[~2013-10-11 13:25 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-09 21:29 [Bridge] [PATCH v2 tip/core/rcu 0/13] Sparse-related updates for 3.13 Paul E. McKenney
2013-10-09 21:29 ` Paul E. McKenney
2013-10-09 21:29 ` Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 01/13] rcu: Make rcu_assign_pointer's assignment volatile and type-safe Paul E. McKenney
2013-10-09 21:29 ` [PATCH v2 tip/core/rcu 02/13] notifiers: Apply rcu_access_pointer() to avoid sparse false positive Paul E. McKenney
2013-10-09 21:29 ` [Bridge] [PATCH v2 tip/core/rcu 03/13] bridge: " Paul E. McKenney
2013-10-09 21:29 ` Paul E. McKenney
2013-10-09 21:29 ` Paul E. McKenney
2013-10-09 21:29 ` [Bridge] [PATCH v2 tip/core/rcu 04/13] wireless: " Paul E. McKenney
2013-10-09 21:29 ` 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
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 [this message]
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 ` [Bridge] [PATCH v2 tip/core/rcu 11/13] bridge/br_mdb: " Paul E. McKenney
2013-10-09 21:29 ` Paul E. McKenney
2013-10-09 21:29 ` Paul E. McKenney
2013-10-09 21:29 ` [Bridge] [PATCH v2 tip/core/rcu 12/13] bonding/bond_main: " Paul E. McKenney
2013-10-09 21:29 ` Paul E. McKenney
2013-10-09 21:29 ` 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 22:26 ` [PATCH v2 tip/core/rcu 01/13] rcu: Make rcu_assign_pointer's assignment volatile and type-safe Josh Triplett
2013-10-09 22:18 ` [Bridge] [PATCH v2 tip/core/rcu 0/13] Sparse-related updates for 3.13 Josh Triplett
2013-10-09 22:18 ` Josh Triplett
2013-10-09 22:46 ` [Bridge] " Paul E. McKenney
2013-10-09 22:46 ` Paul E. McKenney
2013-10-09 22:46 ` Paul E. McKenney
2013-10-09 22:23 ` [Bridge] " Josh Triplett
2013-10-09 22:23 ` Josh Triplett
2013-10-09 22:30 ` [Bridge] " Josh Triplett
2013-10-09 22:30 ` Josh Triplett
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