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

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Message-ID: <1300228944.2565.19.camel@edumazet-laptop>
Date:	Tue, 15 Mar 2011 23:42:24 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	SystemTap <systemtap@...rces.redhat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 2.6.38-rc8-tip 4/20] 4: uprobes: Adding and remove a
 uprobe in a rb tree.

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).



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