thp: change pmd_trans_huge_lock() interface to return ptl

After THP refcounting rework we have only two possible return values
from pmd_trans_huge_lock(): success and failure.  Return-by-pointer for
ptl doesn't make much sense in this case.

Let's convert pmd_trans_huge_lock() to return ptl on success and NULL on
failure.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Minchan Kim <minchan@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index cfe81e1..459fd25 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -120,15 +120,15 @@
 				    unsigned long start,
 				    unsigned long end,
 				    long adjust_next);
-extern bool __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
-		spinlock_t **ptl);
+extern spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd,
+		struct vm_area_struct *vma);
 /* mmap_sem must be held on entry */
-static inline bool pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
-		spinlock_t **ptl)
+static inline spinlock_t *pmd_trans_huge_lock(pmd_t *pmd,
+		struct vm_area_struct *vma)
 {
 	VM_BUG_ON_VMA(!rwsem_is_locked(&vma->vm_mm->mmap_sem), vma);
 	if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd))
-		return __pmd_trans_huge_lock(pmd, vma, ptl);
+		return __pmd_trans_huge_lock(pmd, vma);
 	else
 		return false;
 }
@@ -190,10 +190,10 @@
 					 long adjust_next)
 {
 }
-static inline bool pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
-		spinlock_t **ptl)
+static inline spinlock_t *pmd_trans_huge_lock(pmd_t *pmd,
+		struct vm_area_struct *vma)
 {
-	return false;
+	return NULL;
 }
 
 static inline int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,