linux-kernel - Re: Why I want PTRACE_O

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Date:	Sat, 10 Sep 2011 01:09:58 +0200
From:	"Indan Zupancic" <indan@....nu>
To:	"Oleg Nesterov" <oleg@...hat.com>
Cc:	"Denys Vlasenko" <vda.linux@...glemail.com>,
	"Tejun Heo" <tj@...nel.org>,
	"Denys Vlasenko" <dvlasenk@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Why I want PTRACE_O_TRACESTOP option

On Fri, September 9, 2011 18:26, Oleg Nesterov wrote:
> On 09/09, Indan Zupancic wrote:
>>
>> It is very useful to set options atomically at SEIZE time.
>
> Nobody argues with this.
>
>> Another important reason to make PTRACE_O_TRACESTOP an option is
>> because not everyone uses SEIZE: Users using PTRACE_TRACEME can't
>> set this option at all.
>
> Yes. This was already discussed, PTRACE_TRACEME obviously doesn't
> work if you need the new features. So far it was decided TRACEME
> should be avoided,

How do you want to attach/seize a just forked child without races
in a less ugly way than with TRACEME?

> but perhaps we can add SEIZE_ME. And, unlike
> TRACEME it should probably stop immediately to simplify the
> synchronization with parent. Afaik, any user of TRACEME does
> something like kill(getpid(), SIGSTOP), this doesn't look very
> good.

I let the child send a SIGTERM to itself, so if anything goes wrong
it terminates. It's only needed because you have to set options.

>
> But personally I'd prefer to avoid SEIZE_ME.

Me too. There is no need for it if PTRACE_O_TRACESTOP exists.

Alternatively, if you do want to add it, just allow PTRACE_SEIZE
with zero/own PID to achieve the same.

Greetings,

Indan


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