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

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/util.c b/mm/util.c
index 7b6608d..093c973 100644 (file)
--- a/mm/util.c
+++ b/mm/util.c
@@ -183,17 +183,14 @@ 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();
        }