Add a pmdp_huge_clear_flush() stub for configs that don't define
CONFIG_TRANSPARENT_HUGEPAGE.

We use a WARN_ON_ONCE() instead of a BUILD_BUG() because in the DAX code at
least we do want this compile successfully even for configs without
CONFIG_TRANSPARENT_HUGEPAGE.  It'll be a runtime decision whether we call
this code gets called, based on whether we find DAX PMD entries in our
tree.  We shouldn't ever find such PMD entries for
!CONFIG_TRANSPARENT_HUGEPAGE configs, so this function should never be
called.

Signed-off-by: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
---
 include/asm-generic/pgtable.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 18af2bc..65e9536 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h

@@ -178,9 +178,19 @@ extern pte_t ptep_clear_flush(struct vm_area_struct *vma,
 #endif
 
 #ifndef __HAVE_ARCH_PMDP_HUGE_CLEAR_FLUSH
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 extern pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma,
 			      unsigned long address,
 			      pmd_t *pmdp);
+#else
+static inline pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma,
+			      unsigned long address,
+			      pmd_t *pmdp)
+{
+	WARN_ON_ONCE(1);
+	return *pmdp;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
 #ifndef __HAVE_ARCH_PTEP_SET_WRPROTECT

-- 
2.7.4