[3.13.y.z extended stable] Patch "vm_is_stack: use for_each_thread() rather then buggy while_each_thread()" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    vm_is_stack: use for_each_thread() rather then buggy while_each_thread()

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.7.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From adb734b4effae71eb08df3a8610b22ffc629203c Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg at 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()

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