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-rw-r--r--mm/swapfile.c42
1 files changed, 34 insertions, 8 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 35e00c3d0286..02ccab5ad9d9 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -507,11 +507,23 @@ unsigned int count_swap_pages(int type, int free)
507 * just let do_wp_page work it out if a write is requested later - to 507 * just let do_wp_page work it out if a write is requested later - to
508 * force COW, vm_page_prot omits write permission from any private vma. 508 * force COW, vm_page_prot omits write permission from any private vma.
509 */ 509 */
510static int unuse_pte(struct vm_area_struct *vma, pte_t *pte, 510static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
511 unsigned long addr, swp_entry_t entry, struct page *page) 511 unsigned long addr, swp_entry_t entry, struct page *page)
512{ 512{
513 spinlock_t *ptl;
514 pte_t *pte;
515 int ret = 1;
516
513 if (mem_cgroup_charge(page, vma->vm_mm, GFP_KERNEL)) 517 if (mem_cgroup_charge(page, vma->vm_mm, GFP_KERNEL))
514 return -ENOMEM; 518 ret = -ENOMEM;
519
520 pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
521 if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
522 if (ret > 0)
523 mem_cgroup_uncharge_page(page);
524 ret = 0;
525 goto out;
526 }
515 527
516 inc_mm_counter(vma->vm_mm, anon_rss); 528 inc_mm_counter(vma->vm_mm, anon_rss);
517 get_page(page); 529 get_page(page);
@@ -524,7 +536,9 @@ static int unuse_pte(struct vm_area_struct *vma, pte_t *pte,
524 * immediately swapped out again after swapon. 536 * immediately swapped out again after swapon.
525 */ 537 */
526 activate_page(page); 538 activate_page(page);
527 return 1; 539out:
540 pte_unmap_unlock(pte, ptl);
541 return ret;
528} 542}
529 543
530static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, 544static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
@@ -533,21 +547,33 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
533{ 547{
534 pte_t swp_pte = swp_entry_to_pte(entry); 548 pte_t swp_pte = swp_entry_to_pte(entry);
535 pte_t *pte; 549 pte_t *pte;
536 spinlock_t *ptl;
537 int ret = 0; 550 int ret = 0;
538 551
539 pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); 552 /*
553 * We don't actually need pte lock while scanning for swp_pte: since
554 * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
555 * page table while we're scanning; though it could get zapped, and on
556 * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
557 * of unmatched parts which look like swp_pte, so unuse_pte must
558 * recheck under pte lock. Scanning without pte lock lets it be
559 * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
560 */
561 pte = pte_offset_map(pmd, addr);
540 do { 562 do {
541 /* 563 /*
542 * swapoff spends a _lot_ of time in this loop! 564 * swapoff spends a _lot_ of time in this loop!
543 * Test inline before going to call unuse_pte. 565 * Test inline before going to call unuse_pte.
544 */ 566 */
545 if (unlikely(pte_same(*pte, swp_pte))) { 567 if (unlikely(pte_same(*pte, swp_pte))) {
546 ret = unuse_pte(vma, pte++, addr, entry, page); 568 pte_unmap(pte);
547 break; 569 ret = unuse_pte(vma, pmd, addr, entry, page);
570 if (ret)
571 goto out;
572 pte = pte_offset_map(pmd, addr);
548 } 573 }
549 } while (pte++, addr += PAGE_SIZE, addr != end); 574 } while (pte++, addr += PAGE_SIZE, addr != end);
550 pte_unmap_unlock(pte - 1, ptl); 575 pte_unmap(pte - 1);
576out:
551 return ret; 577 return ret;
552} 578}
553 579