Re: [PATCH v2 2.6.38-rc8-tip 4/20] 4: uprobes: Adding and remove a uprobe in a rb tree.

Eric Dumazet
2011-03-15T22:42:44Z

Le mardi 15 mars 2011 à 20:48 +0100, Peter Zijlstra a écrit :
> On Tue, 2011-03-15 at 20:22 +0100, Thomas Gleixner wrote:
> > I am not sure if its a good idea to walk the tree
> > > as and when the tree is changing either because of a insertion or
> > > deletion of a probe.
> >
> > I know that you cannot walk the tree lockless except you would use
> > some rcu based container for your probes.
>
> You can in fact combine a seqlock, rb-trees and RCU to do lockless
> walks.
>
> https://lkml.org/lkml/2010/10/20/160
>
> and
>
> https://lkml.org/lkml/2010/10/20/437
>
> But doing that would be an optimization best done once we get all this
> working nicely.
>

We have such schem in net/ipv4/inetpeer.c function inet_getpeer() (using
a seqlock on latest net-next-2.6 tree), but we added a counter to make
sure a reader could not enter an infinite loop while traversing tree
(AVL tree in inetpeer case).