[PATCH 1/2] Take rcu read lock when iterating through thread group

[Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>]

Protect the iteration through thread group with rcu_read_lock when
looking for tasks in the group that use the current vma as
stack. Thanks KOSAKI Motohiro (kosaki.motohiro@gmail.com) for pointing
it out.

Signed-off-by: Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>
---
 mm/memory.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 601a920..a88b764 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3915,20 +3915,27 @@ void print_vma_addr(char *prefix, unsigned long ip)
  * just check in the current task.
  */
 int vm_is_stack(struct task_struct *task,
-			      struct vm_area_struct *vma, int in_group)
+		struct vm_area_struct *vma, int in_group)
 {
+	int ret = 0;
+
 	if (vm_is_stack_for_task(task, vma))
 		return 1;
 
 	if (in_group) {
 		struct task_struct *t = task;
+		rcu_read_lock();
 		while_each_thread(task, t) {
-			if (vm_is_stack_for_task(t, vma))
-				return 1;
+			if (vm_is_stack_for_task(t, vma)) {
+				ret = 1;
+				goto done;
+			}
 		}
 	}
 
-	return 0;
+done:
+	rcu_read_unlock();
+	return ret;
 }
 
 #ifdef CONFIG_PROVE_LOCKING
-- 
1.7.7.4