linux-kernel - Re: [PATCH] man ptrace: add extended description of various ptrace quirks

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Message-ID: <CAKgNAkj8STLfO2t5gejct+yPFkFtFtojVkYKJREiE7S2QHSctg@mail.gmail.com>
Date:	Wed, 21 Sep 2011 07:10:44 +0200
From:	Michael Kerrisk <mtk.manpages@...il.com>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Michael Kerrisk <mtk.manpages@...glemail.com>
Subject: Re: [PATCH] man ptrace: add extended description of various ptrace quirks

Denys,

On Thu, Jul 21, 2011 at 6:51 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 07/21, Denys Vlasenko wrote:
>>
>> Deleted several outright false statements:
>> - pid 1 can be traced
>> - tracer is not shown as parent in ps output
>> - PTRACE_ATTACH is not "the same behavior as if tracee had done
>>   a PTRACE_TRACEME": PTRACE_ATTACH delivers a SIGSTOP.
>> - SIGSTOP _can_ be injected.
>
> Yes, this is correct, thanks.
>
>> +Tracer can not assume that tracee ALWAYS ends its life by reporting
>> +WIFEXITED(status) or WIFSIGNALED(status).
>> +.LP
>> +.\" or can it? Do we include such a promise into ptrace API?
>
> IIRC, we already discussed this... The traced group leader can
> disappear during mt-exec, otherwise the tracee can never go away
> silently.
>
>> +Tracer can kill a tracee with ptrace(PTRACE_KILL, pid, 0, 0). This
>> +operation is deprecated, use kill(SIGKILL) or tgkill(SIGKILL) instead.
>> +The problem with this operation is that it requires tracee to be in
>> +signal-delivery-stop, otherwise it may not work (may complete
>> +successfully but won't kill the tracee),
>
> In short, ptrace(PTRACE_KILL) is more or less ptrace(PTRACE_CONT, SIGKILL),
> but it always returns 0. IOW, it never worked as decribed in the man
> page. And I guess today nobody can explain why PTRACE_KILL exists.
>
> Oleg.

Does your patch need any revision in the light of Oleg's comments?

Thanks,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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