Merge branch 'akpm' (Andrew's incoming - part two)

[pandora-kernel.git] / mm / swap.c

diff --git a/mm/swap.c b/mm/swap.c
index 3a442f1..87627f1 100644 (file)
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -78,39 +78,22 @@ static void put_compound_page(struct page *page)
 {
        if (unlikely(PageTail(page))) {
                /* __split_huge_page_refcount can run under us */
-               struct page *page_head = page->first_page;
-               smp_rmb();
-               /*
-                * If PageTail is still set after smp_rmb() we can be sure
-                * that the page->first_page we read wasn't a dangling pointer.
-                * See __split_huge_page_refcount() smp_wmb().
-                */
-               if (likely(PageTail(page) && get_page_unless_zero(page_head))) {
+               struct page *page_head = compound_trans_head(page);
+
+               if (likely(page != page_head &&
+                          get_page_unless_zero(page_head))) {
                        unsigned long flags;
                        /*
-                        * Verify that our page_head wasn't converted
-                        * to a a regular page before we got a
-                        * reference on it.
+                        * page_head wasn't a dangling pointer but it
+                        * may not be a head page anymore by the time
+                        * we obtain the lock. That is ok as long as it
+                        * can't be freed from under us.
                         */
-                       if (unlikely(!PageHead(page_head))) {
-                               /* PageHead is cleared after PageTail */
-                               smp_rmb();
-                               VM_BUG_ON(PageTail(page));
-                               goto out_put_head;
-                       }
-                       /*
-                        * Only run compound_lock on a valid PageHead,
-                        * after having it pinned with
-                        * get_page_unless_zero() above.
-                        */
-                       smp_mb();
-                       /* page_head wasn't a dangling pointer */
                        flags = compound_lock_irqsave(page_head);
                        if (unlikely(!PageTail(page))) {
                                /* __split_huge_page_refcount run before us */
                                compound_unlock_irqrestore(page_head, flags);
                                VM_BUG_ON(PageHead(page_head));
-                       out_put_head:
                                if (put_page_testzero(page_head))
                                        __put_single_page(page_head);
                        out_put_single:
@@ -121,16 +104,17 @@ static void put_compound_page(struct page *page)
                        VM_BUG_ON(page_head != page->first_page);
                        /*
                         * We can release the refcount taken by
-                        * get_page_unless_zero now that
-                        * split_huge_page_refcount is blocked on the
-                        * compound_lock.
+                        * get_page_unless_zero() now that
+                        * __split_huge_page_refcount() is blocked on
+                        * the compound_lock.
                         */
                        if (put_page_testzero(page_head))
                                VM_BUG_ON(1);
                        /* __split_huge_page_refcount will wait now */
-                       VM_BUG_ON(atomic_read(&page->_count) <= 0);
-                       atomic_dec(&page->_count);
+                       VM_BUG_ON(page_mapcount(page) <= 0);
+                       atomic_dec(&page->_mapcount);
                        VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
+                       VM_BUG_ON(atomic_read(&page->_count) != 0);
                        compound_unlock_irqrestore(page_head, flags);
                        if (put_page_testzero(page_head)) {
                                if (PageHead(page_head))
@@ -160,6 +144,45 @@ void put_page(struct page *page)
 }
 EXPORT_SYMBOL(put_page);
 
+/*
+ * This function is exported but must not be called by anything other
+ * than get_page(). It implements the slow path of get_page().
+ */
+bool __get_page_tail(struct page *page)
+{
+       /*
+        * This takes care of get_page() if run on a tail page
+        * returned by one of the get_user_pages/follow_page variants.
+        * get_user_pages/follow_page itself doesn't need the compound
+        * lock because it runs __get_page_tail_foll() under the
+        * proper PT lock that already serializes against
+        * split_huge_page().
+        */
+       unsigned long flags;
+       bool got = false;
+       struct page *page_head = compound_trans_head(page);
+
+       if (likely(page != page_head && get_page_unless_zero(page_head))) {
+               /*
+                * page_head wasn't a dangling pointer but it
+                * may not be a head page anymore by the time
+                * we obtain the lock. That is ok as long as it
+                * can't be freed from under us.
+                */
+               flags = compound_lock_irqsave(page_head);
+               /* here __split_huge_page_refcount won't run anymore */
+               if (likely(PageTail(page))) {
+                       __get_page_tail_foll(page, false);
+                       got = true;
+               }
+               compound_unlock_irqrestore(page_head, flags);
+               if (unlikely(!got))
+                       put_page(page_head);
+       }
+       return got;
+}
+EXPORT_SYMBOL(__get_page_tail);
+
 /**
  * put_pages_list() - release a list of pages
  * @pages: list of pages threaded on page->lru