linux-kernel - Re: [RFC, PATCH] handle the multi-threaded init's exit() properly

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Message-ID: <20070807063431.GB23036@us.ibm.com>
Date:	Mon, 6 Aug 2007 23:34:31 -0700
From:	sukadev@...ibm.com
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...sign.ru>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, containers@...ts.osdl.org,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [RFC, PATCH] handle the multi-threaded init's exit() properly

Andrew Morton [akpm@...ux-foundation.org] wrote:
| On Tue, 7 Aug 2007 00:33:26 +0400 Oleg Nesterov <oleg@...sign.ru> wrote:
| 
| > On 08/06, Andrew Morton wrote:
| > >
| > > On Fri, 3 Aug 2007 01:20:09 +0400 Oleg Nesterov <oleg@...sign.ru> wrote:
| > > 
| > > > 2. We are playing games with ->nsproxy->pid_ns. This code is bogus today, and
| > > >    it has to be changed anyway when we really support pid namespaces, just
| > > >    remove it.
| > >
| > > This patch broke
| > > 
| > > pid-namespaces-define-and-use-task_active_pid_ns-wrapper.patch.  This hunk:
| > > 
| > > ***************
| > > *** 908,915 ****
| > >   	if (unlikely(!tsk->pid))
| > >   		panic("Attempted to kill the idle task!");
| > >   	if (unlikely(tsk == child_reaper(tsk))) {
| > > - 		if (tsk->nsproxy->pid_ns != &init_pid_ns)
| > > - 			tsk->nsproxy->pid_ns->child_reaper = init_pid_ns.child_reaper;
| > >   		else
| > >   			panic("Attempted to kill init!");
| > >   	}
| > > --- 908,916 ----
| > >   	if (unlikely(!tsk->pid))
| > >   		panic("Attempted to kill the idle task!");
| > >   	if (unlikely(tsk == child_reaper(tsk))) {
| > > + 		if (task_active_pid_ns(tsk) != &init_pid_ns)
| > > + 			task_active_pid_ns(tsk)->child_reaper =
| > > + 					init_pid_ns.child_reaper;
| > >   		else
| > >   			panic("Attempted to kill init!");
| > >   	}
| > > 
| > > has no place to live any more, so I just removed it.
| > 
| > Ah, thanks. I should have done this patch against -mm tree.
| > 
| > I hope it is OK to drop this chunk of
| > 	pid-namespaces-define-and-use-task_active_pid_ns-wrapper.patch
| > 
| > Because it can't work right now anyway, and Sukadev+Pavel already have
| > new patches on top this one which make namespace switch actually work.
| > 
| 
| OK, well I had to make a bit of on-the-fly adjustment to
| pid-namespaces-rename-child_reaper-function.patch as well.
| 
| The diff-of-the-diff is:
| 
| @@ -48,7 +48,7 @@
|  diff -puN kernel/exit.c~pid-namespaces-rename-child_reaper-function kernel/exit.c
|  --- a/kernel/exit.c~pid-namespaces-rename-child_reaper-function
|  +++ a/kernel/exit.c
| -@@ -694,7 +694,7 @@ forget_original_parent(struct task_struc
| +@@ -683,7 +683,7 @@ forget_original_parent(struct task_struc
|   	do {
|   		reaper = next_thread(reaper);
|   		if (reaper == father) {
| @@ -57,19 +57,10 @@
|   			break;
|   		}
|   	} while (reaper->exit_state);
| -@@ -907,7 +907,7 @@ fastcall NORET_TYPE void do_exit(long co
| - 		panic("Aiee, killing interrupt handler!");
| - 	if (unlikely(!tsk->pid))
| - 		panic("Attempted to kill the idle task!");
| --	if (unlikely(tsk == child_reaper(tsk))) {
| -+	if (unlikely(tsk == task_child_reaper(tsk))) {
| - 		if (task_active_pid_ns(tsk) != &init_pid_ns)
| - 			task_active_pid_ns(tsk)->child_reaper =
| - 					init_pid_ns.child_reaper;
|  diff -puN kernel/signal.c~pid-namespaces-rename-child_reaper-function kernel/signal.c
| 
| Hopefully people can re-review and retest what's there in next -mm.
| 
| Or if that's too much work or too risky, option b) is to drop
| handle-the-multi-threaded-inits-exit-properly.patch, go back to the
| 2.6.23-rc1-mm2 versions of
| pid-namespaces-define-and-use-task_active_pid_ns-wrapper.patch and
| pid-namespaces-rename-child_reaper-function.patch and to ask Oleg to cook a 2.6.23-rc1-mm2 version of handle-the-multi-threaded-inits-exit-properly.patch.
| 
| The downside of this approach is that
| handle-the-multi-threaded-inits-exit-properly.patch looks more 2.6.24-ready
| than all the container stuff (based just on overall impact and
| speculativeness)

Well, if it will help, we can drop these two patches from -mm, take Oleg's
patch and I can then resend these along with other pid ns patches. 

	pid-namespaces-define-and-use-task_active_pid_ns-wrapper.patch.
	pid-namespaces-rename-child_reaper-function.patch
Suka
-
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