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Date: Wed, 09 Oct 2013 16:17:55 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Josh Triplett <josh@...htriplett.org> Cc: paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org, mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, 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 15:56 -0700, Josh Triplett wrote: > I'd be really hesitant to introduce that type of direct assignment to an > __rcu pointer without wrapping it in some appropriately named macro, or > at the very least adding a comment. Well, there is no special magic here, in this specific case : - deleting an item in an rcu list Check list_del_rcu(), and you'll notice there is no _barrier_ Adding correct barriers is good, but please do not add them when not needed. It makes code hard to understand. ACCESS(*ptr) = value; is clear and autodocumented, because it highlights the potential problem, that is *ptr can be read without any barrier from another cpu. So we ask the compiler to not write temporary garbage in it. rcu_assign_pointer(*ptr, rcu_access_pointer(value)) is very confusing, because it hides the _real_ problem and add defensive programming tricks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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