oom: remove unnecessary code and cleanup

Remove the redundancy in __oom_kill_task() since:

 - init can never be passed to this function: it will never be PF_EXITING
   or selectable from select_bad_process(), and

 - it will never be passed a task from oom_kill_task() without an ->mm
   and we're unconcerned about detachment from exiting tasks, there's no
   reason to protect them against SIGKILL or access to memory reserves.

Also moves the kernel log message to a higher level since the verbosity is
not always emitted here; we need not print an error message if an exiting
task is given a longer timeslice.

__oom_kill_task() only has a single caller, so it can be merged into that
function at the same time.

Signed-off-by: David Rientjes <rientjes@google.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

@@ -410,61 +410,25 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
 }
 
 #define K(x) ((x) << (PAGE_SHIFT-10))
-
-/*
- * Send SIGKILL to the selected  process irrespective of  CAP_SYS_RAW_IO
- * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
- * set.
- */
-static void __oom_kill_task(struct task_struct *p, int verbose)
-{
-	if (is_global_init(p)) {
-		WARN_ON(1);
-		printk(KERN_WARNING "tried to kill init!\n");
-		return;
-	}
-
-	p = find_lock_task_mm(p);
-	if (!p)
-		return;
-
-	if (verbose)
-		printk(KERN_ERR "Killed process %d (%s) "
-		       "vsz:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
-		       task_pid_nr(p), p->comm,
-		       K(p->mm->total_vm),
-		       K(get_mm_counter(p->mm, MM_ANONPAGES)),
-		       K(get_mm_counter(p->mm, MM_FILEPAGES)));
-	task_unlock(p);
-
-	/*
-	 * We give our sacrificial lamb high priority and access to
-	 * all the memory it needs. That way it should be able to
-	 * exit() and clear out its resources quickly...
-	 */
-	p->rt.time_slice = HZ;
-	set_tsk_thread_flag(p, TIF_MEMDIE);
-
-	force_sig(SIGKILL, p);
-}
-
 static int oom_kill_task(struct task_struct *p)
 {
-	/* WARNING: mm may not be dereferenced since we did not obtain its
-	 * value from get_task_mm(p).  This is OK since all we need to do is
-	 * compare mm to q->mm below.
-	 *
-	 * Furthermore, even if mm contains a non-NULL value, p->mm may
-	 * change to NULL at any time since we do not hold task_lock(p).
-	 * However, this is of no concern to us.
-	 */
-	if (!p->mm || p->signal->oom_adj == OOM_DISABLE)
+	p = find_lock_task_mm(p);
+	if (!p || p->signal->oom_adj == OOM_DISABLE) {
+		task_unlock(p);
 		return 1;
+	}
+	pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
+		task_pid_nr(p), p->comm, K(p->mm->total_vm),
+		K(get_mm_counter(p->mm, MM_ANONPAGES)),
+		K(get_mm_counter(p->mm, MM_FILEPAGES)));
+	task_unlock(p);
 
-	__oom_kill_task(p, 1);
-
+	p->rt.time_slice = HZ;
+	set_tsk_thread_flag(p, TIF_MEMDIE);
+	force_sig(SIGKILL, p);
 	return 0;
 }
+#undef K
 
 static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 			    unsigned long points, struct mem_cgroup *mem,