linux-kernel - Re: [PATCH 4/7] uretprobes: return probe entry, prepare

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Message-ID: <20130326085009.GC22603@bandura.brq.redhat.com>
Date:	Tue, 26 Mar 2013 09:50:09 +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>,
	adrian.m.negreanu@...el.com, Torsten.Polle@....de
Subject: Re: [PATCH 4/7] uretprobes: return probe entry, prepare_uretprobe()

On Tue, Mar 26, 2013 at 09:45:33AM +0100, Anton Arapov wrote:
> On Sun, Mar 24, 2013 at 04:26:51PM +0100, Oleg Nesterov wrote:
> > On 03/22, Anton Arapov wrote:
> [snip]
> > And ->dirty looks confusing... perhaps ->chained ?
> > 
> > 		ri = kzalloc(...);
> > 		if (!ri)
> > 			return;
> > 
> > 		ret_vaddr = arch_uretprobe_hijack_return_addr(...);
> > 		if (ret_vaddr == -1)
> > 			goto err;
> > 
> > 		if (ret_vaddr == trampoline_vaddr) {
> > 			if (!utask->return_instances) {
> > 				// This situation is not possible.
> > 				// (not sure we should send SIGSEGV)
> > 				pr_warn(...);
> > 				goto err;
> > 			}
> 
>   If we don't send SIGSEGV, does it make sense to restore the original
> return address that was just hijacked? So that we just decline setting
> the breakpoint for this very case.

disregard this one. we have no address to restore at that moment. :) 

> Anton.
> 
> > 
> > 			ri->chained = true;
> > 			ret_vaddr = utask->return_instances->orig_ret_vaddr;
> > 		}
> > 
> > 		fill-ri-and-add-push-it;
> > 		return;
> > 
> > 	err:
> > 		kfree(ri);
> > 		return;
> > 
> > Oleg.
> > 
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