From 4449a51a7c281602d3a385044ab928322a122a02 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Fri, 8 Aug 2014 14:19:17 -0700
Subject: vm_is_stack: use for_each_thread() rather then buggy while_each_thread()

From: Oleg Nesterov <oleg@redhat.com>

commit 4449a51a7c281602d3a385044ab928322a122a02 upstream.

Aleksei hit the soft lockup during reading /proc/PID/smaps.  David
investigated the problem and suggested the right fix.

while_each_thread() is racy and should die, this patch updates
vm_is_stack().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Aleksei Besogonov <alex.besogonov@gmail.com>
Tested-by: Aleksei Besogonov <alex.besogonov@gmail.com>
Suggested-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/util.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/mm/util.c
+++ b/mm/util.c
@@ -275,17 +275,14 @@ pid_t vm_is_stack(struct task_struct *ta
 
 	if (in_group) {
 		struct task_struct *t;
-		rcu_read_lock();
-		if (!pid_alive(task))
-			goto done;
 
-		t = task;
-		do {
+		rcu_read_lock();
+		for_each_thread(task, t) {
 			if (vm_is_stack_for_task(t, vma)) {
 				ret = t->pid;
 				goto done;
 			}
-		} while_each_thread(task, t);
+		}
 done:
 		rcu_read_unlock();
 	}