[PATCH 3.13 171/187] vm_is_stack: use for_each_thread() rather then buggy while_each_thread()

[Kamal Mostafa]

3.13.11.7 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg at 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 at redhat.com>
Reported-by: Aleksei Besogonov <alex.besogonov at gmail.com>
Tested-by: Aleksei Besogonov <alex.besogonov at gmail.com>
Suggested-by: David Rientjes <rientjes at google.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 mm/util.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 8636d3d..89abc97 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -276,17 +276,14 @@ pid_t vm_is_stack(struct task_struct *task,
 
 	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();
 	}
-- 
1.9.1