On Tue, May 13, 2014 at 10:45:50AM +0100, Mel Gorman wrote:
> void unlock_page(struct page *page)
> {
> + wait_queue_head_t *wqh = clear_page_waiters(page);
> +
> VM_BUG_ON_PAGE(!PageLocked(page), page);
> +
> + /*
> + * No additional barrier needed due to clear_bit_unlock barriering all updates
> + * before waking waiters
> + */
> clear_bit_unlock(PG_locked, &page->flags);
> - smp_mb__after_clear_bit();
> - wake_up_page(page, PG_locked);
This is wrong. The smp_mb__after_clear_bit() is still required to ensure
that the cleared bit is visible before the wakeup on all architectures.
---8<---
diff --git a/mm/filemap.c b/mm/filemap.c
index 6ac066e..028b5a1 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -819,11 +819,8 @@ void unlock_page(struct page *page)
VM_BUG_ON_PAGE(!PageLocked(page), page);
- /*
- * No additional barrier needed due to clear_bit_unlock barriering all updates
- * before waking waiters
- */
clear_bit_unlock(PG_locked, &page->flags);
+ smp_mb__after_clear_bit();
/*
* Wake the queue if waiters were detected. Ordinarily this wakeup
--
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