From: Oleg Nesterov <oleg@redhat.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.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>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Thiago Macieira <thiago.macieira@intel.com>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
linux-fsdevel@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH v2 5/7] clone4: Add a CLONE_AUTOREAP flag to automatically reap the child process
Date: Fri, 20 Mar 2015 19:14:04 +0100 [thread overview]
Message-ID: <20150320181404.GA26343@redhat.com> (raw)
In-Reply-To: <20150315233439.GA31890@thin>
Josh,
I am really sorry for delay.
On 03/15, Josh Triplett wrote:
>
> On Sun, Mar 15, 2015 at 08:55:06PM +0100, Oleg Nesterov wrote:
>
> > It should be per-process simply because this "autoreap" affects the whole
> > process. And the sub-threads are already "autoreap". And these 2 autoreap's
> > semantics differ, we should not confuse them.
>
> Will the approach I suggested, of having clones with CLONE_THREAD
> inherit the autoreap value rather than setting it from CLONE_AUTOREAP,
> implement the semantics you're looking for?
Not sure I understand... CLONE_THREAD should not inherit the autoreap.
A sub-thread is always autoreapable.
> Also, are you suggesting that CLONE_AUTOREAP with CLONE_THREAD should
> produce -EINVAL, or just that it should be ignored?
Yes, I think CLONE_AUTOREAP | CLONE_THREAD should return -EINVAL. But
this all is minor...
The main problem is how/when we should check this "autoreap" without
making this code even more ugly.
I still think we need a preparation patch. I tried to make it today but
failed. Will try again on weekend...
Note that we can't solely rely on do_notify_parent() which (with your patch)
correctly checks !ptrace && autoreap.
Just for example. Please look at __ptrace_detach(). Note that if we add
CLONE_AUTOREAP this needs a fix in any case. The tracee can be "autoreap"
but zombie, because "autoreap" should be ignored until the tracer detaches.
But the "same_thread_group" should not call do_notify_parent() again. So
this needs another check.
And let me quote our discussion from the previous email:
> > EXCEPT: do we really want SIGCHLD from the exiting child? I think we
> > do not. I won't really argue though, but this should be discussed and
> > documented. IIUC, with your patch it is still sent.
>
> I think we do, yes. The caller of clone can already specify what signal
> they want, including no signal at all. If they specify a signal
> (SIGCHLD or otherwise) along with CLONE_AUTOREAP, we can send that
> signal.
OK. Agreed.
Yes, I agree...
But the changes in __ptrace_detach() depend on whether we need to send a signal
or not. Either way the changle is simple, but looks ugly. It would be nice to
cleanup this somehow.
Also. I forgot that the kernel always resets ->exit_signal to SIGCHLD on exec
or reparenting. Reparenting is probably fine. But what about exec? Should it
keep ->exit_signal == 0 if "autoreap" ? I think it should not, to avoid the
strange special case.
> > > > And there are ptrace/mt issues,
> > > > it seems. Just for example, we should avoid EXIT_TRACE if autoreap in
> > > > wait_task_zombie() even if we are going to re-notify parent.
> > >
> > > I don't see how EXIT_TRACE can happen in wait_task_zombie if autoreap is
> > > set. wait_task_zombie does a cmpxchg with exit_state and doesn't
> > > proceed unless exit_state was EXIT_ZOMBIE, and I don't see how we can
> > > ever reach the EXIT_ZOMBIE state if autoreap.
> >
> > Because you again forgot about ptrace ;)
And this too asks for preparation before CLONE_AUTOREAP...
So I'll try to think about this all again on weekend. I'll try very much
to not disappear again ;)
Oleg.
next prev parent reply other threads:[~2015-03-20 18:16 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-15 7:59 [PATCH v2 0/7] CLONE_FD: Task exit notification via file descriptor Josh Triplett
2015-03-15 7:59 ` [PATCH v2 1/7] clone: Support passing tls argument via C rather than pt_regs magic Josh Triplett
2015-03-15 7:59 ` [PATCH v2 2/7] x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit and 64-bit Josh Triplett
2015-03-15 7:59 ` [PATCH v2 3/7] Introduce a new clone4 syscall with more flag bits and extensible arguments Josh Triplett
2015-03-23 14:11 ` David Drysdale
2015-03-23 15:05 ` josh
2015-03-31 14:41 ` David Drysdale
2015-03-15 7:59 ` [PATCH v2 4/7] kernel/fork.c: Pass arguments to _do_fork and copy_process using clone4_args Josh Triplett
2015-03-15 8:00 ` [PATCH v2 5/7] clone4: Add a CLONE_AUTOREAP flag to automatically reap the child process Josh Triplett
2015-03-15 14:52 ` Oleg Nesterov
2015-03-15 17:18 ` Josh Triplett
2015-03-15 19:55 ` Oleg Nesterov
2015-03-15 23:34 ` Josh Triplett
2015-03-20 18:14 ` Oleg Nesterov [this message]
2015-03-20 18:46 ` Thiago Macieira
2015-03-20 19:09 ` Oleg Nesterov
2015-03-20 21:10 ` josh
2015-03-15 8:00 ` [PATCH v2 6/7] signal: Factor out a helper function to process task_struct exit_code Josh Triplett
2015-03-15 8:00 ` [PATCH v2 7/7] clone4: Add a CLONE_FD flag to get task exit notification via fd Josh Triplett
2015-03-23 17:38 ` David Drysdale
2015-03-25 14:53 ` Josh Triplett
2015-04-06 8:30 ` Sergey Senozhatsky
2015-04-06 9:31 ` Josh Triplett
2015-03-15 8:00 ` [PATCH v2 man-pages] clone4.2: New manpage documenting clone4(2) Josh Triplett
2015-03-15 8:04 ` [PATCH v2 0/7] CLONE_FD: Task exit notification via file descriptor Josh Triplett
2015-03-16 21:44 ` Kees Cook
2015-03-16 22:14 ` Thiago Macieira
2015-03-16 22:36 ` Kees Cook
2015-03-16 22:50 ` Thiago Macieira
2015-03-16 23:26 ` Kees Cook
2015-03-16 23:35 ` josh
2015-03-16 23:29 ` josh
2015-03-17 0:49 ` Thiago Macieira
2015-03-23 14:12 ` David Drysdale
2015-03-23 15:03 ` josh
2015-03-16 23:25 ` josh
2015-03-31 20:08 ` Jonathan Corbet
2015-03-31 22:02 ` josh
2015-04-01 7:24 ` Jonathan Corbet
2015-04-09 2:19 ` Josh Triplett
2015-05-29 7:43 ` Florian Weimer
2015-05-29 20:27 ` Thiago Macieira
2015-06-15 10:06 ` Florian Weimer
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