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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Message-ID: <20110126083743.GC19725@linux.vnet.ibm.com>
Date:	Wed, 26 Jan 2011 14:07:43 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
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>,
	Linux-mm <linux-mm@...ck.org>,
	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.

> > +       spin_lock_irqsave(&treelock, flags);
> > +       while (*p) {
> > +               parent = *p;
> > +               u = rb_entry(parent, struct uprobe, rb_node);
> > +               if (u->inode > uprobe->inode)
> > +                       p = &(*p)->rb_left;
> > +               else if (u->inode < uprobe->inode)
> > +                       p = &(*p)->rb_right;
> > +               else {
> > +                       if (u->offset > uprobe->offset)
> > +                               p = &(*p)->rb_left;
> > +                       else if (u->offset < uprobe->offset)
> > +                               p = &(*p)->rb_right;
> > +                       else {
> > +                               atomic_inc(&u->ref);
> 
> If the lookup can find a 'dead' entry, then why can't we here?
> 

If a new user of a uprobe comes up as when the last registered user was
removing the uprobe, we keep the uprobe entry till the new user
loses interest in that uprobe.

> > +                               goto unlock_return;
> > +                       }
> > +               }
> > +       }
> > +       u = NULL;
> > +       rb_link_node(&uprobe->rb_node, parent, p);
> > +       rb_insert_color(&uprobe->rb_node, &uprobes_tree);
> > +       atomic_set(&uprobe->ref, 2);
> > +
> > +unlock_return:
> > +       spin_unlock_irqrestore(&treelock, flags);
> > +       return u;
> > +} 
> 
> It would be nice if you could merge the find and 'acquire' thing, the
> lookup is basically the same in both cases.
> 
> Also, I'm not quite sure on the name of that last function, its not a
> strict insert and what's the trailing _rb_node about? That lookup isn't
> called find_uprobe_rb_node() either is it?

Since we already have a install_uprobe, register_uprobe, I thought
insert_uprobe_rb_node would give context to that function that it was
only inserting an rb_node but not installing the actual breakpoint.
I am okay to rename it to insert_uprobe(). 
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