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

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Date:	Wed, 9 Jan 2013 17:17:01 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anton Arapov <anton@...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 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.

>  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.

Oleg.

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