[vpsAdminOS] oom_kill exceptions for CT init & lxc

OOM killer in vpsAdminOS container should never kill its init, as is true
for normal full Linux boxes.

Also let's make an exception for lxc-start responsible for the container's
lifetime.

Signed-off-by: Pavel Snajdr <snajpa@snajpa.net>

mm/oom_kill.c

@@ -200,6 +200,8 @@ unsigned long oom_badness(struct task_struct *p, unsigned long totalpages)
 {
 	long points;
 	long adj;
+	struct pid_namespace *ns;
+	pid_t ns_pid;
 
 	if (oom_unkillable_task(p))
 		return 0;
@@ -214,6 +216,21 @@ unsigned long oom_badness(struct task_struct *p, unsigned long totalpages)
 	 * the middle of vfork
 	 */
 	adj = (long)p->signal->oom_score_adj;
+
+	ns = task_active_pid_ns(p);
+	ns_pid = task_pid_nr_ns(p, ns);
+
+	if (((p->cred->user_ns == &init_user_ns) &&
+	     (ns == &init_pid_ns) &&
+	     (strcmp(p->comm, "lxc-start") == 0)
+	    ) ||
+	    ((p->cred->user_ns->parent == &init_user_ns) &&
+	     (ns != &init_pid_ns) &&
+	     (ns_pid == 1)
+	    )
+	  )
+		adj = (long)OOM_SCORE_ADJ_MIN;
+
 	if (adj == OOM_SCORE_ADJ_MIN ||
 			test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
 			in_vfork(p)) {