linux-kernel - Re: [PATCH 07/10] uprobes/x86: Introduce arch_uretprobe_is

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Message-ID: <20150520155156.GA1343@redhat.com>
Date:	Wed, 20 May 2015 17:51:56 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pratyush Anand <panand@...hat.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <arapov@...il.com>,
	David Long <dave.long@...aro.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jan Willeke <willeke@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Mark Wielaard <mjw@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/10] uprobes/x86: Introduce arch_uretprobe_is_alive()

Hi Pratyush,

sorry for delay, vacation.

On 05/18, Pratyush Anand wrote:
> Hi Oleg,
>
> On Monday 04 May 2015 06:19 PM, Oleg Nesterov wrote:
>> +bool __weak arch_uretprobe_is_alive(struct arch_uretprobe *auret, struct pt_regs *regs)
>> +{
>> +	return true;
>> +}
>
> IIUC, then this function should return false when both auret and regs
> are corresponding to same retprobe, else we need to return true, right?

Not sure I understand what you mean...

This function should return false when we know that this return_instance
was invalidated by longjmp().

> If that is the case, then should n't following work for all the cases:
>
> return sp != auret->sp;

No, this can't work.

On x86 "sp == auret->sp" only right after the "call" insn, the stack
can grow after that but this does not mean that this instance is no
longer valid.

Oleg.

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