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

[sukadev at us.ibm.com]

Pavel Emelianov [xemul at openvz.org] wrote:
| 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_?

I agree its not strictly needed for pid namespace. If there is another
need for a 'task list', pid namespace could also be optimized to use the
list.
| 
| > 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]

Yes - at least for now.

| 
| 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.

Ok. But is there a need that all tasks completely exit before the
container-init ? Note that we change the reaper for the namespace to
/sbin/init before we start terminating processes.


| 
| > +	}
| > +	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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