linux-kernel - Re: [RFC PATCH v3 5/6] uretprobes: invoke return probe handlers

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Date:	Sat, 2 Mar 2013 19:09:39 +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 v3 5/6] uretprobes: invoke return probe handlers

On 02/28, Anton Arapov wrote:
>
> @@ -1576,8 +1622,8 @@ static void handle_swbp(struct pt_regs *regs)
>  
>  	if (!uprobe) {
>  		if (is_swbp > 0) {
> -			/* No matching uprobe; signal SIGTRAP. */
> -			send_sig(SIGTRAP, current, 0);
> +			/* No matching uprobe; Try with uretprobe */
> +			handle_uretprobe(regs);

Hmm. at least this looks certainly wrong.

You shifted send_sig(SIGSEGV) into handle_uretprobe(), but if nothing
else printk(KERN_ERR "uprobe: no instance found!") doesn't look nice
if we hit the regular breakoint.

In fact everything handle_uretprobe() does in this case looks wrong.
Including the fact that get_xol_area/get_utask can fail. And unwinding
looks bogus...

I think you need

	if (bp_vaddr == rp_trampoline_vaddr)
		handle_uretprobe()

like the previous version did.

Oleg.

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