rk: revert 20f3d0b+v3.0.66 to v3.0

[firefly-linux-kernel-4.4.55.git] / mm / swap.c

diff --git a/mm/swap.c b/mm/swap.c
index 4a1fc6db89e8a2153130f6f21eb9eda85937b6d7..3a442f18b0b3dab5acfd99b5fc4e85389b9b5439 100644 (file)
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -78,22 +78,39 @@ static void put_compound_page(struct page *page)
 {
        if (unlikely(PageTail(page))) {
                /* __split_huge_page_refcount can run under us */
-               struct page *page_head = compound_trans_head(page);
-
-               if (likely(page != page_head &&
-                          get_page_unless_zero(page_head))) {
+               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))) {
                        unsigned long flags;
                        /*
-                        * 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.
+                        * Verify that our page_head wasn't converted
+                        * to a a regular page before we got a
+                        * reference on it.
                         */
+                       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:
@@ -104,17 +121,16 @@ 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(page_mapcount(page) <= 0);
-                       atomic_dec(&page->_mapcount);
+                       VM_BUG_ON(atomic_read(&page->_count) <= 0);
+                       atomic_dec(&page->_count);
                        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))
@@ -144,45 +160,6 @@ 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
@@ -667,7 +644,7 @@ void lru_add_page_tail(struct zone* zone,
        VM_BUG_ON(!PageHead(page));
        VM_BUG_ON(PageCompound(page_tail));
        VM_BUG_ON(PageLRU(page_tail));
-       VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&zone->lru_lock));
+       VM_BUG_ON(!spin_is_locked(&zone->lru_lock));
 
        SetPageLRU(page_tail);