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>

3 files changed, 20 insertions, 13 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8ad580273521..2d1ffe9d0e26 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1560,7 +1560,8 @@ int madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	struct mm_struct *mm = tlb->mm;
 	int ret = 0;
 
-	if (!pmd_trans_huge_lock(pmd, vma, &ptl))
+	ptl = pmd_trans_huge_lock(pmd, vma);
+	if (!ptl)
 		goto out_unlocked;
 
 	orig_pmd = *pmd;
@@ -1627,7 +1628,8 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	pmd_t orig_pmd;
 	spinlock_t *ptl;
 
-	if (!__pmd_trans_huge_lock(pmd, vma, &ptl))
+	ptl = __pmd_trans_huge_lock(pmd, vma);
+	if (!ptl)
 		return 0;
 	/*
 	 * For architectures like ppc64 we look at deposited pgtable
@@ -1690,7 +1692,8 @@ bool move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
 	 * We don't have to worry about the ordering of src and dst
 	 * ptlocks because exclusive mmap_sem prevents deadlock.
 	 */
-	if (__pmd_trans_huge_lock(old_pmd, vma, &old_ptl)) {
+	old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
+	if (old_ptl) {
 		new_ptl = pmd_lockptr(mm, new_pmd);
 		if (new_ptl != old_ptl)
 			spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
@@ -1724,7 +1727,8 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 	spinlock_t *ptl;
 	int ret = 0;
 
-	if (__pmd_trans_huge_lock(pmd, vma, &ptl)) {
+	ptl = __pmd_trans_huge_lock(pmd, vma);
+	if (ptl) {
 		pmd_t entry;
 		bool preserve_write = prot_numa && pmd_write(*pmd);
 		ret = 1;
@@ -1760,14 +1764,14 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
  * Note that if it returns true, this routine returns without unlocking page
  * table lock. So callers must unlock it.
  */
-bool __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
-		spinlock_t **ptl)
+spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
 {
-	*ptl = pmd_lock(vma->vm_mm, pmd);
+	spinlock_t *ptl;
+	ptl = pmd_lock(vma->vm_mm, pmd);
 	if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
-		return true;
-	spin_unlock(*ptl);
-	return false;
+		return ptl;
+	spin_unlock(ptl);
+	return NULL;
 }
 
 #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ca052f2a4a0b..d06cae2de783 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4638,7 +4638,8 @@ static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,
 	pte_t *pte;
 	spinlock_t *ptl;
 
-	if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
+	ptl = pmd_trans_huge_lock(pmd, vma);
+	if (ptl) {
 		if (get_mctgt_type_thp(vma, addr, *pmd, NULL) == MC_TARGET_PAGE)
 			mc.precharge += HPAGE_PMD_NR;
 		spin_unlock(ptl);
@@ -4826,7 +4827,8 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
 	union mc_target target;
 	struct page *page;
 
-	if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
+	ptl = pmd_trans_huge_lock(pmd, vma);
+	if (ptl) {
 		if (mc.precharge < HPAGE_PMD_NR) {
 			spin_unlock(ptl);
 			return 0;
diff --git a/mm/mincore.c b/mm/mincore.c
index 2a565ed8bb49..563f32045490 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -117,7 +117,8 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 	unsigned char *vec = walk->private;
 	int nr = (end - addr) >> PAGE_SHIFT;
 
-	if (pmd_trans_huge_lock(pmd, vma, &ptl)) {
+	ptl = pmd_trans_huge_lock(pmd, vma);
+	if (ptl) {
 		memset(vec, 1, nr);
 		spin_unlock(ptl);
 		goto out;