linux-kernel - Re: [RFC PATCH v4 5/6] uretprobes: invoke return probe handlers

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Date:	Tue, 5 Mar 2013 14:28:05 +0100
From:	Anton Arapov <anton@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Stone <jistone@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [RFC PATCH v4 5/6] uretprobes: invoke return probe handlers

On Mon, Mar 04, 2013 at 05:51:20PM +0100, Oleg Nesterov wrote:
> On 03/04, Anton Arapov wrote:
> >
> > +static void handle_uretprobe(struct xol_area *area, struct pt_regs *regs)
> > +{
> > +	struct hlist_head *head;
> > +	struct hlist_node *tmp;
> > +	struct return_uprobe_i *ri;
> > +	struct uprobe_task *utask;
> > +	unsigned long orig_ret_vaddr;
> > +
> > +	/* TODO: uretprobe bypass logic */
> > +
> > +	utask = get_utask();
> > +	if (!utask) {
> > +		/* TODO:RFC task is not probed, do we want printk here? */
> > +		return;
> > +	}
> > +	head = &utask->return_uprobes;
> > +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> > +		if (ri->uprobe->consumers) {
> > +			instruction_pointer_set(regs, ri->orig_ret_vaddr);
> This doesn't look right if ri->orig_ret_vaddr == area->vaddr. We should
> splice the list and find orig_ret_vaddr in advance.
True, this cycle is buggy. I will rework handle_uretprobe().

> > @@ -1589,8 +1639,11 @@ static void handle_swbp(struct pt_regs *regs)
> >
> >  	if (!uprobe) {
> >  		if (is_swbp > 0) {
> > -			/* No matching uprobe; signal SIGTRAP. */
> > -			send_sig(SIGTRAP, current, 0);
> > +			area = get_xol_area();
> > +			if (area && bp_vaddr == area->vaddr)
> > +				handle_uretprobe(area, regs);
> > +			else
> > +				send_sig(SIGTRAP, current, 0);
> 
> Why? We can check bp_vaddr at the start, before find_active_uprobe().
For some reason, I was thinking it is better to hide this logic under
if (!uprobe). Will correct this chunk.

> And I'd suggest to not use area->vaddr directly, imho a trivial helper
> makes sense.
I see the idea behind, with this change it will be more clear and
fragile in case someone change the underneath logic. Will do this.

thank you very much!
Anton.
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