[PATCH] mm: add rcu read lock to protect pid structure

[<zeng.zhaoming@freescale.com>]

From: Zeng Zhaoming <zengzm.kernel@gmail.com>

find_task_by_vpid should be protected by rcu_read_lock(),
to prevent free_pid() reclaiming pid.

Signed-off-by: Zeng Zhaoming <zengzm.kernel@gmail.com>
---
 mm/mempolicy.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 81a1276..ceaf0d8 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1307,15 +1307,18 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
 		goto out;
 
 	/* Find the mm_struct */
+	rcu_read_lock();
 	read_lock(&tasklist_lock);
 	task = pid ? find_task_by_vpid(pid) : current;
 	if (!task) {
 		read_unlock(&tasklist_lock);
+		rcu_read_unlock();
 		err = -ESRCH;
 		goto out;
 	}
 	mm = get_task_mm(task);
 	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 
 	err = -EINVAL;
 	if (!mm)
-- 
1.7.0.4


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