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

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Date:	Tue, 19 Apr 2011 20:54:09 +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 20:29, Oleg Nesterov wrote:
>> I'll try to check these patches from the correctness pov tomorrow,
>> but to be honest I hope someone will nack them before I start ;)
> OK, I briefly looked at 3/3. It looks certainly wrong.
>
> 	notif = do_signal_parent(...);
> 	if (notif != DEATH_REAP) {
> 	....
>
> 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?

> Also. I didn't actually read the patch yet, but iiuc: if a task T does
> PR_DETACH and then exits, init can't reap it until the old parent does
> wait. This can confuse the poor admin, he can see the zombies with
> ppid = 1 and there is no way to understand why.
Oh my. :)) I guess you are not going to suggest a solution to
that "problem", other than to rip the patch? :)
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