mm: page lock use lock bitops
trylock_page, unlock_page open and close a critical section. Hence,
we can use the lock bitops to get the desired memory ordering.
Also, mark trylock as likely to succeed (and remove the annotation from
callers).
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/filemap.c b/mm/filemap.c
index a1ddd25..e1b23fd 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -573,17 +573,14 @@
* mechananism between PageLocked pages and PageWriteback pages is shared.
* But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
*
- * The first mb is necessary to safely close the critical section opened by the
- * test_and_set_bit() to lock the page; the second mb is necessary to enforce
- * ordering between the clear_bit and the read of the waitqueue (to avoid SMP
- * races with a parallel wait_on_page_locked()).
+ * The mb is necessary to enforce ordering between the clear_bit and the read
+ * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
*/
void unlock_page(struct page *page)
{
- smp_mb__before_clear_bit();
- if (!test_and_clear_bit(PG_locked, &page->flags))
- BUG();
- smp_mb__after_clear_bit();
+ VM_BUG_ON(!PageLocked(page));
+ clear_bit_unlock(PG_locked, &page->flags);
+ smp_mb__after_clear_bit();
wake_up_page(page, PG_locked);
}
EXPORT_SYMBOL(unlock_page);