linux-kernel - Re: ptrace.2: PTRACE_KILL needs a stopped process too

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Message-ID: <20120509201219.GA32051@redhat.com>
Date:	Wed, 9 May 2012 22:12:19 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pedro Alves <palves@...hat.com>
Cc:	Mike Frysinger <vapier@...too.org>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	pacman@...h.dhis.org, linux-man <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Tejun Heo <tj@...nel.org>,
	Jan Kratochvil <jan.kratochvil@...hat.com>
Subject: Re: ptrace.2: PTRACE_KILL needs a stopped process too

On 05/09, Pedro Alves wrote:
>
> On 05/09/2012 04:09 PM, Mike Frysinger wrote:
>
> > probably not that big of a deal, but the reason i like using
> > ptrace(PTRACE_KILL) over a raw kill() is that you are less likely to kill the
> > wrong process by accident.  maybe not that big of a deal in practice though.
>
>
> And you can do tgkill instead.  It was specifically invented to handle the
> reuse case.

tgkill() can kill the wrong process/thread too, although it lessens the risk.

But I don't really understand the problem. The traced thread can't go away
until the tracer does wait/detach, and thus its pid can't be reused?

May be, "by accident" above means something else, not pid reuse...

Oleg.

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