[Devel] [PATCH 12/17] Pid-NS(V3) Terminate processes in a ns when reaper is exiting.

[Pavel Emelianov]

sukadev at us.ibm.com wrote:
> Subject: [PATCH 12/17] Pid-NS(V3) Terminate processes in a ns when reaper is exiting.
> 
> From: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> 
> This should actually be considered a part of the previous patch which
> enables cloning of pid namespace. Its been separated out for easier
> review.
> 
> Terminate all processes in a namespace when the reaper of the namespace
> is exiting. We do this by walking the pidmap of the namespace and sending
> SIGKILL to all processes.
> 
> TODO:
> 	- Consider maintaining a per-pid namespace tasklist. Use that list
> 	  to terminate processes in the namespace more efficiently. Such a 
> 	  tasklist may also be useful to freeze or checkpoint an application.

Pid namespace of its own can happily live without this. 
Why is this needed _for_the_namespace_?

> Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> ---
>  include/linux/pid.h           |    1 +
>  include/linux/pid_namespace.h |    1 +
>  kernel/exit.c                 |    5 +++--
>  kernel/fork.c                 |   19 +++++++++++++++++++
>  kernel/pid.c                  |   42 ++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 66 insertions(+), 2 deletions(-)
> 

[snip]

> Index: lx26-22-rc4-mm2/kernel/pid.c
> ===================================================================
> --- lx26-22-rc4-mm2.orig/kernel/pid.c	2007-06-15 18:52:19.000000000 -0700
> +++ lx26-22-rc4-mm2/kernel/pid.c	2007-06-15 18:52:19.000000000 -0700
> @@ -145,6 +145,9 @@ static int alloc_pidmap(struct pid_names
>  	int i, offset, max_scan, pid, last = pid_ns->last_pid;
>  	struct pidmap *map;
>  
> +	if (atomic_read(&pid_ns->terminating))
> +		return -1;
> +
>  	pid = last + 1;
>  	if (pid >= pid_max)
>  		pid = RESERVED_PIDS;
> @@ -314,6 +317,39 @@ static struct pid_namespace *alloc_pid_n
>  	return ns;
>  }
>  
> +/*
> + * When child reaper of the pid namespace @pid_ns is itself terminating,
> + * we need to terminate all processes in the pid namespace since /proc
> + * has a reference to the child reaper of the pid namespace.
> + *
> + * Send SIGKILL to all processes in the pid namespace. Set the 'terminating'
> + * flag in pid_ns to prevent any new processes from getting created in the
> + * pid namespace.
> + *
> + * Note that we will also be terminating all our child pid namespaces
> + * (if any) since we send SIGKILL their reapers as well.
> + *
> + * TODO: It maybe more efficient to maintain a list of tasks in the
> + *       pid namespace and walk that list.
> + */
> +void zap_pid_ns_processes(struct pid_namespace *pid_ns)
> +{
> +	int nr;
> +
> +	atomic_set(&pid_ns->terminating, 1);
> +
> +	/*
> +	 * We know pid == 1 is terminating. Find remaining pid_ts
> +	 * in the namespace and terminate them.
> +	 */
> +	nr = next_pidmap(pid_ns, 1);
> +	while (nr > 0) {
> +		kill_proc(nr, SIGKILL, 1);
> +		nr = next_pidmap(pid_ns, nr);

This looks like a proc_flush_task():
[cite]
 * NOTE: This routine is just an optimization so it does not guarantee
 *       that no ... (processes) will exist at process exit time it
 *       just makes it very unlikely that any will persist.
[/cite]

If we really want the namespace to be terminated right when its leader (init)
exits we have to do_wait() for each killed task and resend the signals.

> +	}
> +	return;
> +}
> +
>  #else
>  
>  static struct pid_namespace *alloc_pid_ns(void)
> @@ -321,6 +357,12 @@ static struct pid_namespace *alloc_pid_n
>  	WARN_ON_ONCE(1);
>  	return ERR_PTR(-EINVAL);
>  }
> +
> +void zap_pid_ns_processes(struct pid_namespace *pid_ns)
> +{
> +	/* Nothing to do when we don't have multiple pid namespaces */
> +	return;
> +}
>  #endif 	/*CONFIG_PID_NS*/
>  
>  static inline struct kmem_cache *select_pid_cache(int num_upids)
> 

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