mempolicy: remove tasklist_lock from migrate_pages

Today, tasklist_lock in migrate_pages doesn't protect anything.
rcu_read_lock() provide enough protection from pid hash walk.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reported-by: Peter Zijlstra <peterz@infradead.org>
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>

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 7ee55af8d79cb120c9f9209c5b37f36a369d26c4..e6d351265aede4c598fe70ee6a9586c1a0e91e92 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1310,16 +1310,13 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
 
        /* 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;