pidns: use kzalloc when allocating new pid_namespace struct

It makes many fields initialization implicit helping in auto-setting
#ifdef-ed fields (bsd-acct related pointer will be such).

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/pid_namespace.c

@@ -71,7 +71,7 @@ static struct pid_namespace *create_pid_namespace(unsigned int level)
 	struct pid_namespace *ns;
 	int i;
 
-	ns = kmem_cache_alloc(pid_ns_cachep, GFP_KERNEL);
+	ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
 	if (ns == NULL)
 		goto out;
 
@@ -84,17 +84,13 @@ static struct pid_namespace *create_pid_namespace(unsigned int level)
 		goto out_free_map;
 
 	kref_init(&ns->kref);
-	ns->last_pid = 0;
-	ns->child_reaper = NULL;
 	ns->level = level;
 
 	set_bit(0, ns->pidmap[0].page);
 	atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
 
-	for (i = 1; i < PIDMAP_ENTRIES; i++) {
-		ns->pidmap[i].page = NULL;
+	for (i = 1; i < PIDMAP_ENTRIES; i++)
 		atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
-	}
 
 	return ns;