From: Josh Triplett <josh@joshtriplett.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Thiago Macieira <thiago.macieira@intel.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@amacapital.net>,
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>,
Michael Kerrisk <mtk.manpages@gmail.com>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
linux-fsdevel@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit notification via fd
Date: Sat, 14 Mar 2015 13:03:18 -0700 [thread overview]
Message-ID: <20150314200318.GG22130@thin> (raw)
In-Reply-To: <20150314191836.GA8416@redhat.com>
On Sat, Mar 14, 2015 at 08:18:36PM +0100, Oleg Nesterov wrote:
> On 03/14, Josh Triplett wrote:
> >
> > On Sat, Mar 14, 2015 at 11:38:29AM -0700, Thiago Macieira wrote:
> > > On Saturday 14 March 2015 15:32:35 Oleg Nesterov wrote:
> > > > 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?
> > >
> > > It should ignore the child that is set to autoreap. wait(NULL) should return -
> > > ECHILD, indicating there are no children waiting to be reaped.
> >
> > Right. And I don't think the current code does this. I think we need
> > to change wait_consider_task to early-return for ->autoreap just as it
> > does for task_state == EXIT_DEAD.
>
> No. This EXIT_DEAD is absolutely different. And this is another indication
> that you might use it wrongly ;)
Is there any information somewhere on how this state machine of doom is
*supposed* to work? :) Why would "p->task_state == EXIT_DEAD" mean
something different in wait_consider_task?
> What we actually want is BUG_ON(task_state == EXIT_DEAD) here. We do not
> want the EXIT_DEAD tasks in ->children/ptraced lists. These EXIT_DEAD tasks
> complicate the exit/wait/reparent paths.
Pulling the EXIT_DEAD tasks out of those lists completely does sound
like a good simplification. However, that doesn't seem to be the
current expectation in wait_consider_task, which just returns if
p->task_state == EXIT_DEAD to skip considering that task.
And an autoreaping task isn't necessarily dead yet; it just shouldn't be
waited on.
> However, currently this is TODO. The main problem is the locking in
> wait_task_zombie(), we can set EXIT_DEAD and remove the task from list
> under read_lock().
That appears to be only reachable for zombies, which an autoreaping task
should never become.
> And please see another email from me. So far I disagree that wait(NULL)
> should return ECHILD unconditionally. At least unless this is discussed
> separately.
I'll respond in that separate thread, but one issue there: waiting for
any child process cannot safely return an autoreaping child process,
because that would introduce a race condition. The PID the parent gets
back can disappear at any time, so there's nothing useful the parent can
do with it.
- Josh Triplett
next prev parent reply other threads:[~2015-03-14 20:03 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-13 1:40 [PATCH 0/6] CLONE_FD: Task exit notification via file descriptor Josh Triplett
2015-03-13 1:40 ` [PATCH 1/6] clone: Support passing tls argument via C rather than pt_regs magic Josh Triplett
2015-03-13 1:40 ` [PATCH 2/6] x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit and 64-bit Josh Triplett
2015-03-13 22:01 ` Andy Lutomirski
2015-03-13 22:31 ` josh
2015-03-13 22:38 ` Andy Lutomirski
2015-03-13 22:43 ` josh
2015-03-13 22:45 ` Andy Lutomirski
2015-03-13 23:01 ` josh
2015-03-13 1:40 ` [PATCH 3/6] Introduce a new clone4 syscall with more flag bits and extensible arguments Josh Triplett
2015-03-13 1:40 ` [PATCH 4/6] signal: Factor out a helper function to process task_struct exit_code Josh Triplett
2015-03-13 1:40 ` [PATCH 5/6] fs: Make alloc_fd non-private Josh Triplett
2015-03-13 1:41 ` [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit notification via fd Josh Triplett
2015-03-13 16:21 ` Oleg Nesterov
2015-03-13 19:57 ` josh
2015-03-13 21:34 ` Andy Lutomirski
2015-03-13 22:20 ` josh
2015-03-13 22:28 ` Andy Lutomirski
2015-03-13 22:34 ` josh
2015-03-13 22:38 ` Andy Lutomirski
2015-03-14 14:14 ` Oleg Nesterov
2015-03-14 14:32 ` Oleg Nesterov
2015-03-14 18:38 ` Thiago Macieira
2015-03-14 18:54 ` Oleg Nesterov
2015-03-14 22:03 ` Josh Triplett
2015-03-14 22:26 ` Thiago Macieira
2015-03-14 19:01 ` Josh Triplett
2015-03-14 19:18 ` Oleg Nesterov
2015-03-14 19:47 ` Oleg Nesterov
2015-03-14 20:14 ` Josh Triplett
2015-03-14 20:30 ` Oleg Nesterov
2015-03-14 22:14 ` Josh Triplett
2015-03-14 20:03 ` Josh Triplett [this message]
2015-03-14 20:20 ` Oleg Nesterov
2015-03-14 22:09 ` Josh Triplett
2015-03-14 14:35 ` Oleg Nesterov
2015-03-14 19:15 ` Josh Triplett
2015-03-14 19:24 ` Oleg Nesterov
2015-03-14 19:48 ` Josh Triplett
2015-03-13 1:41 ` [PATCH] clone4.2: New manpage documenting clone4(2) Josh Triplett
2015-03-13 2:07 ` [PATCH 0/6] CLONE_FD: Task exit notification via file descriptor Thiago Macieira
2015-03-13 16:05 ` David Drysdale
2015-03-13 19:42 ` Josh Triplett
2015-03-13 21:16 ` Thiago Macieira
2015-03-13 21:44 ` josh
2015-03-13 21:33 ` Andy Lutomirski
2015-03-13 21:45 ` josh
2015-03-13 21:51 ` Andy Lutomirski
2015-03-14 1:11 ` Thiago Macieira
2015-03-14 19:03 ` Thiago Macieira
2015-03-14 19:29 ` Josh Triplett
2015-03-15 10:18 ` David Drysdale
2015-03-15 10:59 ` Josh Triplett
2015-03-15 8:55 ` David Drysdale
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