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;