Messages in this thread | | | Date | Fri, 11 Oct 2013 06:25:12 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2 tip/core/rcu 07/13] ipv6/ip6_tunnel: Apply rcu_access_pointer() to avoid sparse false positive |
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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
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