linux-kernel - Re: [RFC] [PATCH 2.6.37-rc5-tip 4/20] 4: uprobes: Adding and remove a uprobe in a rb tree.

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Date:	Wed, 26 Jan 2011 11:13:21 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.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>,
	Andi Kleen <andi@...stfloor.org>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 4/20]  4: uprobes: Adding and
 remove a uprobe in a rb tree.

On Wed, 2011-01-26 at 14:11 +0530, Srikar Dronamraju wrote:
> * Peter Zijlstra <peterz@...radead.org> [2011-01-25 13:15:42]:
> 
> > On Thu, 2010-12-16 at 15:28 +0530, Srikar Dronamraju wrote:
> > > +/* Should be called lock-less */
> > > +static void put_uprobe(struct uprobe *uprobe)
> > > +{
> > > +       if (atomic_dec_and_test(&uprobe->ref))
> > > +               kfree(uprobe);
> > > +} 
> > 
> > Since this instantly frees the uprobe once ref hits 0, the
> > atomic_inc_not_zero() in find_uprobe() doesn't really make sense does
> > it?
> 
> Okay, I can move the atomic_inc_not_zero() in find_uprobe() to
> atomic_inc().
> 
> Do you see any side-effects of using atomic_inc_not_zero?

No, its just slower, once you want to start doing RCU lookups in the
probe tree you'll need it through.
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