linux-kernel - Re: [PATCH] [RFC] pidns: don't zap processes several times

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Message-ID: <20121007102034.GA1614@gmail.com>
Date:	Sun, 7 Oct 2012 14:20:34 +0400
From:	Andrew Vagin <avagin@...il.com>
To:	Andrew Vagin <avagin@...nvz.org>
Cc:	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] [RFC] pidns: don't zap processes several times

The test program is attached.

On Sun, Oct 07, 2012 at 01:49:18PM +0400, Andrew Vagin wrote:
> I wrote a test program. It does clone(CLONE_NEWPID | CLONE_VM) and
> sleep(), a new task repeates the same actions. This program creates
> 4000 tasks. When I tried to kill all this processes, a system was
> inaccessible for some minutes.
> 
> The system is inaccessible, because each process calls
> zap_pid_ns_processes, which tries to kill subprocesses under
> tasklist_lock. The most time are required for find_vpid().
> 
> I suggest to mark sub-namespaces in zap_pid_ns_processes.
> zap_pid_ns_processes for marked pidns doesn't kill tasks,
> it only waits them.
> 
> I am not sure, that this idea is correct, but it helps.
> 
> Maybe we should restrict depth of pidns?
> Why can't we enumerate task->children instead of using find_vpid()?
> 
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Serge Hallyn <serge.hallyn@...onical.com>
> Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Vasiliy Kulikov <segoon@...nwall.com>
> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Pavel Emelyanov <xemul@...allels.com>
> Signed-off-by: Andrew Vagin <avagin@...nvz.org>
> ---
>  include/linux/pid_namespace.h |    1 +
>  kernel/pid_namespace.c        |   14 ++++++++++++--
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index 00474b0..28073a0 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -34,6 +34,7 @@ struct pid_namespace {
>  	kgid_t pid_gid;
>  	int hide_pid;
>  	int reboot;	/* group exit code if this pidns was rebooted */
> +	atomic_t zapped; /* non zero if all process were killed */
>  };
>  
>  extern struct pid_namespace init_pid_ns;
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index b051fa6..7db7dcd 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -177,21 +177,31 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
>  	 * 	  maintain a tasklist for each pid namespace.
>  	 *
>  	 */
> +
> +	if (atomic_read(&pid_ns->zapped))
> +		goto wait; /* All processes were already killed */
> +
>  	read_lock(&tasklist_lock);
>  	nr = next_pidmap(pid_ns, 1);
>  	while (nr > 0) {
>  		rcu_read_lock();
>  
>  		task = pid_task(find_vpid(nr), PIDTYPE_PID);
> -		if (task && !__fatal_signal_pending(task))
> +		if (task && !__fatal_signal_pending(task)) {
> +			struct pid_namespace *ns;
> +
>  			send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
> +			ns = task_active_pid_ns(task);
> +			if (unlikely(ns->child_reaper == task))
> +				atomic_set(&ns->zapped, 1);
> +		}
>  
>  		rcu_read_unlock();
>  
>  		nr = next_pidmap(pid_ns, nr);
>  	}
>  	read_unlock(&tasklist_lock);
> -
> +wait:
>  	/* Firstly reap the EXIT_ZOMBIE children we may have. */
>  	do {
>  		clear_thread_flag(TIF_SIGPENDING);
> -- 
> 1.7.1
> 
> --
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View attachment "test.c" of type "text/plain" (715 bytes)