mm/mempolicy.c: add rcu read lock to protect pid structure

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>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 4a57f135b76e..11ff260fb282 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)