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-rw-r--r--kernel/futex.c21
1 files changed, 6 insertions, 15 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index aca8d10704f..5e71a6bf6f6 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -201,21 +201,6 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key)
* from swap. But that's a lot of code to duplicate here
* for a rare case, so we simply fetch the page.
*/
-
- /*
- * Do a quick atomic lookup first - this is the fastpath.
- */
- page = follow_page(mm, uaddr, FOLL_TOUCH|FOLL_GET);
- if (likely(page != NULL)) {
- key->shared.pgoff =
- page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
- put_page(page);
- return 0;
- }
-
- /*
- * Do it the general way.
- */
err = get_user_pages(current, mm, uaddr, 1, 0, 0, &page, NULL);
if (err >= 0) {
key->shared.pgoff =
@@ -285,7 +270,13 @@ static void wake_futex(struct futex_q *q)
/*
* The waiting task can free the futex_q as soon as this is written,
* without taking any locks. This must come last.
+ *
+ * A memory barrier is required here to prevent the following store
+ * to lock_ptr from getting ahead of the wakeup. Clearing the lock
+ * at the end of wake_up_all() does not prevent this store from
+ * moving.
*/
+ wmb();
q->lock_ptr = NULL;
}