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mm: cleanup follow_page_mask()
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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>
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Kirill A. Shutemov authored and Linus Torvalds committed Jun 4, 2014
1 parent f2b495c commit 69e68b4
Showing 1 changed file with 119 additions and 112 deletions.
231 changes: 119 additions & 112 deletions mm/gup.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -128,12 +58,14 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
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)) {
Expand Down Expand Up @@ -178,33 +110,108 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
unlock_page(page);
}
}
unlock:
pte_unmap_unlock(ptep, ptl);
out:
return page;

bad_page:
pte_unmap_unlock(ptep, ptl);
return ERR_PTR(-EFAULT);

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)
Expand Down

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