linux-kernel - Re: [path][rfc] add PR_DETACH prctl command [3/3]

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Message-ID: <4DADC92E.3010409@aknet.ru>
Date:	Tue, 19 Apr 2011 21:41:02 +0400
From:	Stas Sergeev <stsp@...et.ru>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [path][rfc] add PR_DETACH prctl command [3/3]

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, because only do_notify_parent()
can do that"? In other words, do_signal_parent() can return
DEATH_REAP after all?
If so - will fix, thanks.

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