Merge pull request #76 from toradex/4.9-2.3.x-imx

4.9 2.3.x imx

1 files changed, 18 insertions, 2 deletions

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 74e4dda91238..896e4199623a 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -545,12 +545,28 @@ static inline int PageTransCompound(struct page *page)
  *
  * Unlike PageTransCompound, this is safe to be called only while
  * split_huge_pmd() cannot run from under us, like if protected by the
- * MMU notifier, otherwise it may result in page->_mapcount < 0 false
+ * MMU notifier, otherwise it may result in page->_mapcount check false
  * positives.
+ *
+ * We have to treat page cache THP differently since every subpage of it
+ * would get _mapcount inc'ed once it is PMD mapped.  But, it may be PTE
+ * mapped in the current process so comparing subpage's _mapcount to
+ * compound_mapcount to filter out PTE mapped case.
  */
 static inline int PageTransCompoundMap(struct page *page)
 {
-	return PageTransCompound(page) && atomic_read(&page->_mapcount) < 0;
+	struct page *head;
+
+	if (!PageTransCompound(page))
+		return 0;
+
+	if (PageAnon(page))
+		return atomic_read(&page->_mapcount) < 0;
+
+	head = compound_head(page);
+	/* File THP is PMD mapped and not PTE mapped */
+	return atomic_read(&page->_mapcount) ==
+	       atomic_read(compound_mapcount_ptr(head));
 }
 
 /*