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

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Date:	Thu,  1 Mar 2012 10:50:58 +0530
From:	Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jamie Lokier <jamie@...reable.org>,
	Mike Frysinger <vapier@...too.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>,
	Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>
Subject: [PATCH 1/2] Take rcu read lock when iterating through thread group

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@...il.com) for pointing
it out.

Signed-off-by: Siddhesh Poyarekar <siddhesh.poyarekar@...il.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

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