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

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Message-ID: <20130326084533.GB22603@bandura.brq.redhat.com>
Date:	Tue, 26 Mar 2013 09:45:33 +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 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.

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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