linux-kernel - Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit notification via fd

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Message-ID: <20150314143235.GA12086@redhat.com>
Date:	Sat, 14 Mar 2015 15:32:35 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	josh@...htriplett.org
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>, Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Thiago Macieira <thiago.macieira@...el.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task
	exit notification via fd

And let me add another note before I forget...

On 03/14, Oleg Nesterov wrote:
>
> On 03/13, josh@...htriplett.org wrote:
> >
> >
> > A process launching a new process with CLONE_FD is explicitly requesting
> > that the process be automatically reaped without any other process
> > having to wait on it.  The task needs to not become a zombie, because
> > otherwise, it'll show up in waitpid(-1, ...)
>
> This is clear.
>
> But please note that this task can be traced/debugged by unrelated process,
> not its real_parent/creator. Say, the system admin does "strace -p". This
> simply breaks the current API.
>
> Again, again, I didn't read this series yet. But the proper solution (afaics)
> should move this "autoreap" check in release_task/__ptrace_detach(). If the
> task is traced. Debugger should check ->autoreap and skip another
> do_notify_parent().
>
> Speaking of autoreap... If ->exit_signal is zero, then the exiting child
> doesn't send the notification to its parent, still it doesn't autoreap
> itself. To me this looks strange, and in fact it seems to me that this
> is only by mistake. I am wondering if we can treat ->exit_signal == 0
> as "autoreap" too. As usual, most probably the answer is "no, because it
> is too late to change the historical behaviour". But this is off-topic.


It is not clear to me what do_wait() should do with ->autoreap child, even
ignoring ptrace.

Just suppose that real_parent has a single "autoreap" child. Should wait(NULL)
hanf then?

If yes, who will wake the parent up?

If no, I do not see the necessary changes in wait_cosnider_task().

Oleg.

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