diff options
| -rw-r--r-- | mm/swapfile.c | 38 |
1 files changed, 31 insertions, 7 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c index f5ba723faf8..14bc4f28a8c 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -506,9 +506,19 @@ unsigned int count_swap_pages(int type, int free) * just let do_wp_page work it out if a write is requested later - to * force COW, vm_page_prot omits write permission from any private vma. */ -static void unuse_pte(struct vm_area_struct *vma, pte_t *pte, +static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr, swp_entry_t entry, struct page *page) { + spinlock_t *ptl; + pte_t *pte; + int found = 1; + + pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); + if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) { + found = 0; + goto out; + } + inc_mm_counter(vma->vm_mm, anon_rss); get_page(page); set_pte_at(vma->vm_mm, addr, pte, @@ -520,6 +530,9 @@ static void unuse_pte(struct vm_area_struct *vma, pte_t *pte, * immediately swapped out again after swapon. */ activate_page(page); +out: + pte_unmap_unlock(pte, ptl); + return found; } static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, @@ -528,22 +541,33 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, { pte_t swp_pte = swp_entry_to_pte(entry); pte_t *pte; - spinlock_t *ptl; int found = 0; - pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); + /* + * We don't actually need pte lock while scanning for swp_pte: since + * we hold page lock and mmap_sem, swp_pte cannot be inserted into the + * page table while we're scanning; though it could get zapped, and on + * some architectures (e.g. x86_32 with PAE) we might catch a glimpse + * of unmatched parts which look like swp_pte, so unuse_pte must + * recheck under pte lock. Scanning without pte lock lets it be + * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE. + */ + pte = pte_offset_map(pmd, addr); do { /* * swapoff spends a _lot_ of time in this loop! * Test inline before going to call unuse_pte. */ if (unlikely(pte_same(*pte, swp_pte))) { - unuse_pte(vma, pte++, addr, entry, page); - found = 1; - break; + pte_unmap(pte); + found = unuse_pte(vma, pmd, addr, entry, page); + if (found) + goto out; + pte = pte_offset_map(pmd, addr); } } while (pte++, addr += PAGE_SIZE, addr != end); - pte_unmap_unlock(pte - 1, ptl); + pte_unmap(pte - 1); +out: return found; } |