mm: cleanup follow_page_mask()

Cleanups:
 - move pte-related code to separate function. It's about half of the
   function;
 - get rid of some goto-logic;
 - use 'return NULL' instead of 'return page' where page can only be
   NULL;

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 119 insertions, 112 deletions

diff --git a/mm/gup.c b/mm/gup.c
index 0bf127b332e7..406367845ded 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -12,105 +12,35 @@
 
 #include "internal.h"
 
-/**
- * follow_page_mask - look up a page descriptor from a user-virtual address
- * @vma: vm_area_struct mapping @address
- * @address: virtual address to look up
- * @flags: flags modifying lookup behaviour
- * @page_mask: on output, *page_mask is set according to the size of the page
- *
- * @flags can have FOLL_ flags set, defined in <linux/mm.h>
- *
- * Returns the mapped (struct page *), %NULL if no mapping exists, or
- * an error pointer if there is a mapping to something not represented
- * by a page descriptor (see also vm_normal_page()).
- */
-struct page *follow_page_mask(struct vm_area_struct *vma,
-                              unsigned long address, unsigned int flags,
-                              unsigned int *page_mask)
+static struct page *no_page_table(struct vm_area_struct *vma,
+                unsigned int flags)
 {
-        pgd_t *pgd;
-        pud_t *pud;
-        pmd_t *pmd;
-        pte_t *ptep, pte;
-        spinlock_t *ptl;
-        struct page *page;
-        struct mm_struct *mm = vma->vm_mm;
-
-        *page_mask = 0;
-
-        page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
-        if (!IS_ERR(page)) {
-                BUG_ON(flags & FOLL_GET);
-                goto out;
-        }
-
-        page = NULL;
-        pgd = pgd_offset(mm, address);
-        if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
-                goto no_page_table;
+        /*
+         * When core dumping an enormous anonymous area that nobody
+         * has touched so far, we don't want to allocate unnecessary pages or
+         * page tables.  Return error instead of NULL to skip handle_mm_fault,
+         * then get_dump_page() will return NULL to leave a hole in the dump.
+         * But we can only make this optimization where a hole would surely
+         * be zero-filled if handle_mm_fault() actually did handle it.
+         */
+        if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault))
+                return ERR_PTR(-EFAULT);
+        return NULL;
+}
 
-        pud = pud_offset(pgd, address);
-        if (pud_none(*pud))
-                goto no_page_table;
-        if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
-                if (flags & FOLL_GET)
-                        goto out;
-                page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
-                goto out;
-        }
-        if (unlikely(pud_bad(*pud)))
-                goto no_page_table;
+static struct page *follow_page_pte(struct vm_area_struct *vma,
+                unsigned long address, pmd_t *pmd, unsigned int flags)
+{
+        struct mm_struct *mm = vma->vm_mm;
+        struct page *page;
+        spinlock_t *ptl;
+        pte_t *ptep, pte;
 
-        pmd = pmd_offset(pud, address);
-        if (pmd_none(*pmd))
-                goto no_page_table;
-        if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
-                page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
-                if (flags & FOLL_GET) {
-                        /*
-                         * Refcount on tail pages are not well-defined and
-                         * shouldn't be taken. The caller should handle a NULL
-                         * return when trying to follow tail pages.
-                         */
-                        if (PageHead(page))
-                                get_page(page);
-                        else {
-                                page = NULL;
-                                goto out;
-                        }
-                }
-                goto out;
-        }
-        if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
-                goto no_page_table;
-        if (pmd_trans_huge(*pmd)) {
-                if (flags & FOLL_SPLIT) {
-                        split_huge_page_pmd(vma, address, pmd);
-                        goto split_fallthrough;
-                }
-                ptl = pmd_lock(mm, pmd);
-                if (likely(pmd_trans_huge(*pmd))) {
-                        if (unlikely(pmd_trans_splitting(*pmd))) {
-                                spin_unlock(ptl);
-                                wait_split_huge_page(vma->anon_vma, pmd);
-                        } else {
-                                page = follow_trans_huge_pmd(vma, address,
-                                                             pmd, flags);
-                                spin_unlock(ptl);
-                                *page_mask = HPAGE_PMD_NR - 1;
-                                goto out;
-                        }
-                } else
-                        spin_unlock(ptl);
-                /* fall through */
-        }
-split_fallthrough:
+retry:
         if (unlikely(pmd_bad(*pmd)))
-                goto no_page_table;
+                return no_page_table(vma, flags);
 
         ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
-
         pte = *ptep;
         if (!pte_present(pte)) {
                 swp_entry_t entry;
@@ -128,12 +58,14 @@ split_fallthrough:
                         goto no_page;
                 pte_unmap_unlock(ptep, ptl);
                 migration_entry_wait(mm, pmd, address);
-                goto split_fallthrough;
+                goto retry;
         }
         if ((flags & FOLL_NUMA) && pte_numa(pte))
                 goto no_page;
-        if ((flags & FOLL_WRITE) && !pte_write(pte))
-                goto unlock;
+        if ((flags & FOLL_WRITE) && !pte_write(pte)) {
+                pte_unmap_unlock(ptep, ptl);
+                return NULL;
+        }
 
         page = vm_normal_page(vma, address, pte);
         if (unlikely(!page)) {
@@ -178,11 +110,8 @@ split_fallthrough:
                         unlock_page(page);
                 }
         }
-unlock:
         pte_unmap_unlock(ptep, ptl);
-out:
         return page;
-
 bad_page:
         pte_unmap_unlock(ptep, ptl);
         return ERR_PTR(-EFAULT);
@@ -190,21 +119,99 @@ bad_page:
 no_page:
         pte_unmap_unlock(ptep, ptl);
         if (!pte_none(pte))
+                return NULL;
+        return no_page_table(vma, flags);
+}
+
+/**
+ * follow_page_mask - look up a page descriptor from a user-virtual address
+ * @vma: vm_area_struct mapping @address
+ * @address: virtual address to look up
+ * @flags: flags modifying lookup behaviour
+ * @page_mask: on output, *page_mask is set according to the size of the page
+ *
+ * @flags can have FOLL_ flags set, defined in <linux/mm.h>
+ *
+ * Returns the mapped (struct page *), %NULL if no mapping exists, or
+ * an error pointer if there is a mapping to something not represented
+ * by a page descriptor (see also vm_normal_page()).
+ */
+struct page *follow_page_mask(struct vm_area_struct *vma,
+                              unsigned long address, unsigned int flags,
+                              unsigned int *page_mask)
+{
+        pgd_t *pgd;
+        pud_t *pud;
+        pmd_t *pmd;
+        spinlock_t *ptl;
+        struct page *page;
+        struct mm_struct *mm = vma->vm_mm;
+
+        *page_mask = 0;
+
+        page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
+        if (!IS_ERR(page)) {
+                BUG_ON(flags & FOLL_GET);
                 return page;
+        }
 
-no_page_table:
-        /*
-         * When core dumping an enormous anonymous area that nobody
-         * has touched so far, we don't want to allocate unnecessary pages or
-         * page tables.  Return error instead of NULL to skip handle_mm_fault,
-         * then get_dump_page() will return NULL to leave a hole in the dump.
-         * But we can only make this optimization where a hole would surely
-         * be zero-filled if handle_mm_fault() actually did handle it.
-         */
-        if ((flags & FOLL_DUMP) &&
-            (!vma->vm_ops || !vma->vm_ops->fault))
-                return ERR_PTR(-EFAULT);
-        return page;
+        pgd = pgd_offset(mm, address);
+        if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+                return no_page_table(vma, flags);
+
+        pud = pud_offset(pgd, address);
+        if (pud_none(*pud))
+                return no_page_table(vma, flags);
+        if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
+                if (flags & FOLL_GET)
+                        return NULL;
+                page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
+                return page;
+        }
+        if (unlikely(pud_bad(*pud)))
+                return no_page_table(vma, flags);
+
+        pmd = pmd_offset(pud, address);
+        if (pmd_none(*pmd))
+                return no_page_table(vma, flags);
+        if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
+                page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
+                if (flags & FOLL_GET) {
+                        /*
+                         * Refcount on tail pages are not well-defined and
+                         * shouldn't be taken. The caller should handle a NULL
+                         * return when trying to follow tail pages.
+                         */
+                        if (PageHead(page))
+                                get_page(page);
+                        else
+                                page = NULL;
+                }
+                return page;
+        }
+        if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
+                return no_page_table(vma, flags);
+        if (pmd_trans_huge(*pmd)) {
+                if (flags & FOLL_SPLIT) {
+                        split_huge_page_pmd(vma, address, pmd);
+                        return follow_page_pte(vma, address, pmd, flags);
+                }
+                ptl = pmd_lock(mm, pmd);
+                if (likely(pmd_trans_huge(*pmd))) {
+                        if (unlikely(pmd_trans_splitting(*pmd))) {
+                                spin_unlock(ptl);
+                                wait_split_huge_page(vma->anon_vma, pmd);
+                        } else {
+                                page = follow_trans_huge_pmd(vma, address,
+                                                             pmd, flags);
+                                spin_unlock(ptl);
+                                *page_mask = HPAGE_PMD_NR - 1;
+                                return page;
+                        }
+                } else
+                        spin_unlock(ptl);
+        }
+        return follow_page_pte(vma, address, pmd, flags);
 }
 
 static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr)