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

From: Andy Lutomirski <luto@amacapital.net>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>, Kees Cook <keescook@chromium.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Rik van Riel <riel@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Thiago Macieira <thiago.macieira@intel.com>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	X86 ML <x86@kernel.org>
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit notification via fd
Date: Fri, 13 Mar 2015 15:28:26 -0700	[thread overview]
Message-ID: <CALCETrVRqgsbpi9pPRwy42cuXiDzyPgWRJmfSRSQM7eGFfsZYA@mail.gmail.com> (raw)
In-Reply-To: <20150313222052.GC10954@cloud>

On Fri, Mar 13, 2015 at 3:20 PM,  <josh@joshtriplett.org> wrote:
> On Fri, Mar 13, 2015 at 02:34:58PM -0700, Andy Lutomirski wrote:
>> On Fri, Mar 13, 2015 at 12:57 PM,  <josh@joshtriplett.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, ...) calls in the parent
>> > process, which would break the ability to use this to completely
>> > encapsulate process management within a library and not interfere with
>> > the parent's process handling via SIGCHLD and wait{pid,3,4}.
>>
>> Wouldn't the correct behavior be to keep it alive as a zombie but
>> *not* show it in waitpid, etc?
>
> That's a significant change to the semantics of waitpid.  And then
> someone would still need to wait on the process, which we'd like to
> avoid.  (We don't want to have magic "reap on read(2)" semantics,
> because among other things, what if we add a means in the future to get
> an additional file descriptor corresponding to an existing process?)
>

Do we not already have a state "dead, successfully waited on by
parent, but still around because ptraced"?  If not, shouldn't we?
Isn't that what PTRACE_SEIZE does?  Or am I just confused?

--Andy