Date: Wed, 9 May 2012 22:12:19 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Pedro Alves <palves@redhat.com>
Cc: Mike Frysinger <vapier@gentoo.org>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        pacman@kosh.dhis.org, linux-man <linux-man@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Denys Vlasenko <dvlasenk@redhat.com>, Tejun Heo <tj@kernel.org>,
        Jan Kratochvil <jan.kratochvil@redhat.com>
Subject: Re: ptrace.2: PTRACE_KILL needs a stopped process too
Message-ID: <20120509201219.GA32051@redhat.com>
References: <20091216004533.22261.qmail@kosh.dhis.org> <CAKgNAkhtu8d0NKcTwWyCA8qWgz8Lag+GcpEE1=YMVe_Nh8XJ9Q@mail.gmail.com> <20120422200459.GA7519@redhat.com> <201205091109.35637.vapier@gentoo.org> <4FAAC706.6000808@redhat.com>
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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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