linux-kernel - Re: [RFC PATCH v2 3/4] uretprobes: return probe entry, prepare uretprobe

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Date:	Thu, 10 Jan 2013 12:44:06 +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 v2 3/4] uretprobes: return probe entry, prepare
 uretprobe

On Wed, Jan 09, 2013 at 05:17:01PM +0100, Oleg Nesterov wrote:
> On 01/09, Anton Arapov wrote:
> >
> > todo:
> >   protect uprobe
> 
> Yep ;)
> 
> >  static struct uprobe_task *get_utask(void)
> >  {
> > -	if (!current->utask)
> > +	if (!current->utask) {
> >  		current->utask = kzalloc(sizeof(struct uprobe_task), GFP_KERNEL);
> > +		INIT_HLIST_HEAD(&current->utask->return_uprobes);
> 
> What if kzalloc() fails?
:)

> 
> > +static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
> > +{
> > +	struct return_uprobe_i *ri;
> > +	struct uprobe_task *utask;
> > +	struct xol_area *area;
> > +	unsigned long rp_trampoline_vaddr = 0;
> > +
> > +	area = get_xol_area();
> > +	if (area)
> > +		rp_trampoline_vaddr = area->rp_trampoline_vaddr;
> > +	if (!rp_trampoline_vaddr) {
> > +		rp_trampoline_vaddr = xol_get_trampoline_slot();
> 
> This is obviously racy. But again, so far I think we can simply remove
> this.
working on this...

> >  static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
> >  {
> > +	int rc = 0;
> >  	struct uprobe_consumer *uc;
> >  	int remove = UPROBE_HANDLER_REMOVE;
> >  
> >  	down_read(&uprobe->register_rwsem);
> >  	for (uc = uprobe->consumers; uc; uc = uc->next) {
> > -		int rc = uc->handler(uc, regs);
> > +		if (uc->handler)
> > +			rc = uc->handler(uc, regs);
> > +
> > +		if (uc->rp_handler)
> > +			prepare_uretprobe(uprobe, regs); /* put bp at return */
> 
> This doesn't look right. prepare_uretprobe() should not be called
> multiple times.
Overlooked this issue, thanks for catching. 

Anton.
> 
> Oleg.
> 
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