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Re: [RFC] [PATCH 2.6.37-rc5-tip 8/20] 8: uprobes: mmap and fork hooks.
- From: Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>
- To: Peter Zijlstra <peterz at infradead dot org>
- Cc: Ingo Molnar <mingo at elte dot hu>, Steven Rostedt <rostedt at goodmis dot org>, Linux-mm <linux-mm at kvack dot org>, Arnaldo Carvalho de Melo <acme at infradead dot org>, Linus Torvalds <torvalds at linux-foundation dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Christoph Hellwig <hch at infradead dot org>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, Oleg Nesterov <oleg at redhat dot com>, LKML <linux-kernel at vger dot kernel dot org>, SystemTap <systemtap at sources dot redhat dot com>, Jim Keniston <jkenisto at linux dot vnet dot ibm dot com>, Frederic Weisbecker <fweisbec at gmail dot com>, Andi Kleen <andi at firstfloor dot org>, Andrew Morton <akpm at linux-foundation dot org>, "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>
- Date: Wed, 26 Jan 2011 20:39:46 +0530
- Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 8/20] 8: uprobes: mmap and fork hooks.
- References: <20101216095714.23751.52601.sendpatchset@localhost6.localdomain6> <20101216095848.23751.73144.sendpatchset@localhost6.localdomain6> <1295957741.28776.719.camel@laptop>
- Reply-to: Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>
* Peter Zijlstra <peterz@infradead.org> [2011-01-25 13:15:41]:
> On Thu, 2010-12-16 at 15:28 +0530, Srikar Dronamraju wrote:
> > +static void search_within_subtree(struct rb_node *n, struct inode *inode,
> > + struct list_head *tmp_list);
> > +
> > +static void add_to_temp_list(struct vm_area_struct *vma, struct inode *inode,
> > + struct list_head *tmp_list)
> > +{
> > + struct uprobe *uprobe;
> > + struct rb_node *n;
> > + unsigned long flags;
> > +
> > + n = uprobes_tree.rb_node;
> > + spin_lock_irqsave(&treelock, flags);
> > + while (n) {
> > + uprobe = rb_entry(n, struct uprobe, rb_node);
> > + if (match_inode(uprobe, inode, &n)) {
> > + list_add(&uprobe->pending_list, tmp_list);
> > + search_within_subtree(n, inode, tmp_list);
> > + break;
> > + }
> > + }
> > + spin_unlock_irqrestore(&treelock, flags);
> > +}
> > +
> > +static void __search_within_subtree(struct rb_node *p, struct inode *inode,
> > + struct list_head *tmp_list)
> > +{
> > + struct uprobe *uprobe;
> > +
> > + uprobe = rb_entry(p, struct uprobe, rb_node);
> > + if (match_inode(uprobe, inode, &p)) {
> > + list_add(&uprobe->pending_list, tmp_list);
> > + search_within_subtree(p, inode, tmp_list);
> > + }
> > +
> > +
> > +}
> > +
> > +static void search_within_subtree(struct rb_node *n, struct inode *inode,
> > + struct list_head *tmp_list)
> > +{
> > + struct rb_node *p;
> > +
> > + if (p)
> > + __search_within_subtree(p, inode, tmp_list);
> > +
> > + p = n->rb_right;
> > + if (p)
> > + __search_within_subtree(p, inode, tmp_list);
> > +}
>
> Whee recursion FTW!, you just blew your kernel stack :-)
>
> Since you sort inode first, offset second, I think you can simply look
> for the first matching inode entry and simply rb_next() until you don't
> match.
Agree that we should get rid of recursion.
I dont think we can simply use rb_next() once we have the first
matching function. There could be a matching inode but a smaller
offset in left that will be missed by rb_next(). (Unless I have
misunderstood rb_next() !!!)
Here are the ways I think we can workaround.
A. change the match_inode() logic to use rb_first/rb_next.
This would make negate the benefit we get from rb_trees because we
have to match every node. Also match_offset might get a little tricky.
B. use the current match_inode but change the search_within_subtree
logic. search_within_subtree() would first find the leftmode node
within the subtree that still has the same inode. Thereafter it will use
rb_next().
Do you have any other ideas?
--
Thanks and Regards
Srikar