From: Oleg Nesterov <oleg@tv-sign.ru>

Add the temporary (for -mm only) debugging code to catch the unbalanced
put_pid()'s.  At least those which can free the "live" pid.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Valdis.Kletnieks@vt.edu
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/pid.c |    4 ++++
 1 file changed, 4 insertions(+)

diff -puN kernel/pid.c~put_pid-make-sure-we-dont-free-the-live-pid kernel/pid.c
--- a/kernel/pid.c~put_pid-make-sure-we-dont-free-the-live-pid
+++ a/kernel/pid.c
@@ -210,6 +210,10 @@ void put_pid(struct pid *pid)
 	ns = pid->numbers[pid->level].ns;
 	if ((atomic_read(&pid->count) == 1) ||
 	     atomic_dec_and_test(&pid->count)) {
+		int type = PIDTYPE_MAX;
+		while (--type >= 0)
+			if (WARN_ON(!hlist_empty(&pid->tasks[type])))
+				return;
 		kmem_cache_free(ns->pid_cachep, pid);
 		put_pid_ns(ns);
 	}
_