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-rw-r--r--mm/swap.c83
1 files changed, 53 insertions, 30 deletions
diff --git a/mm/swap.c b/mm/swap.c
index 3a442f18b0b3..87627f181c3f 100644
--- 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