Date: Tue, 19 Apr 2011 20:17:33 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Stas Sergeev <stsp@aknet.ru>
Cc: Linux kernel <linux-kernel@vger.kernel.org>
Subject: Re: [path][rfc] add PR_DETACH prctl command [3/3]
Message-ID: <20110419181733.GA30702@redhat.com>
References: <20110405164557.GA23248@redhat.com> <4DADA22A.1010205@aknet.ru> <20110419155830.7ad33312@lxorguk.ukuu.org.uk> <4DADA581.9060700@aknet.ru> <20110419165429.71cb1508@lxorguk.ukuu.org.uk> <20110419161301.GA23914@redhat.com> <20110419162909.GC23914@redhat.com> <4DADBE31.7000400@aknet.ru> <20110419172036.GA27213@redhat.com> <4DADC92E.3010409@aknet.ru>
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On 04/19, Stas Sergeev wrote:
>
> 19.04.2011 21:20, Oleg Nesterov wrote:
>
>>>> do_signal_parent() must not return DEATH_REAP (this means that
>>>> leader->exit_signal becomes -1), but this can happen and this is bug.
>>>>
>>> Could you please clarify this a bit: according to the comments
>>> in signal.c:
>>> ---
>>>                   * We are exiting and our parent doesn't care.  POSIX.1
>>>                   * defines special semantics for setting SIGCHLD to SIG_IGN
>>>                   * or setting the SA_NOCLDWAIT flag: we should be reaped
>>>                   * automatically and not left for our parent's wait4 call.
>>> ---
>>> That's how I understand it: if DEATH_REAP is returned, the
>>> parent ignores SIGCHILD, and in this case I am not allowing
>>> it to read the detach code with wait(). What is the bug?
>> Indeed. But, once again, that is why do_notify_parent() expects the dead
>> tsk! Please note that if it returns DEATH_REAP it sets ->exit_signal = -1.
>> And this is _only_ allowed if the leader is already dead and we are going
>> to reap it.
> Ah, so, by saying "do_signal_parent() must not return DEATH_REAP (this means that
> leader->exit_signal becomes -1)", you actually meant
> "do_signal_parent(), when returning DEATH_REAP, must not
> set ->exit_signal = -1,

Yes.

> because only do_notify_parent()
> can do that"?

because we can only do this if we are going to reap the task

> If so - will fix, thanks.

Stas, please do not trim CC. I am very glad Alan looked at this patch,
I hope he will participate. Better yet, add Linus too as I already asked ;)

Oleg.

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