[PATCH 5/8] badpage: zap print_bad_pte on swap and file

Hugh Dickins
2008-12-01T00:44:49Z

Complete zap_pte_range()'s coverage of bad pagetable entries by calling
print_bad_pte() on a pte_file in a linear vma and on a bad swap entry.
That needs free_swap_and_cache() to tell it, which will also have shown
one of those "swap_free" errors (but with much less information).

Similar checks in fork's copy_one_pte()? No, that would be more noisy
than helpful: we'll see them when parent and child exec or exit.

Where do_nonlinear_fault() calls print_bad_pte(): omit !VM_CAN_NONLINEAR
case, that could only be a bug in sys_remap_file_pages(), not a bad pte.
VM_FAULT_OOM rather than VM_FAULT_SIGBUS? Well, okay, that is consistent
with what happens if do_swap_page() operates a bad swap entry; but don't
we have patches to be more careful about killing when VM_FAULT_OOM?

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---

include/linux/swap.h | 12 +++---------
mm/memory.c | 11 +++++++----
mm/swapfile.c | 7 ++++---

--- badpage4/include/linux/swap.h 2008-11-26 12:19:00.000000000 +0000
+++ badpage5/include/linux/swap.h 2008-11-28 20:40:46.000000000 +0000
@@ -305,7 +305,7 @@ extern swp_entry_t get_swap_page_of_type
extern int swap_duplicate(swp_entry_t);
extern int valid_swaphandles(swp_entry_t, unsigned long *);
extern void swap_free(swp_entry_t);
-extern void free_swap_and_cache(swp_entry_t);
+extern int free_swap_and_cache(swp_entry_t);
extern int swap_type_of(dev_t, sector_t, struct block_device **);
extern unsigned int count_swap_pages(int, int);
extern sector_t map_swap_page(struct swap_info_struct *, pgoff_t);
@@ -355,14 +355,8 @@ static inline void show_swap_cache_info(
{
}

-static inline void free_swap_and_cache(swp_entry_t swp)
-{
-}
-
-static inline int swap_duplicate(swp_entry_t swp)
-{
- return 0;
-}
+#define free_swap_and_cache(swp) is_migration_entry(swp)
+#define swap_duplicate(swp) is_migration_entry(swp)

static inline void swap_free(swp_entry_t swp)
{
--- badpage4/mm/memory.c 2008-11-28 20:40:42.000000000 +0000
+++ badpage5/mm/memory.c 2008-11-28 20:40:46.000000000 +0000
@@ -800,8 +800,12 @@ static unsigned long zap_pte_range(struc
*/
if (unlikely(details))
continue;
- if (!pte_file(ptent))
- free_swap_and_cache(pte_to_swp_entry(ptent));
+ if (pte_file(ptent)) {
+ if (unlikely(!(vma->vm_flags & VM_NONLINEAR)))
+ print_bad_pte(vma, addr, ptent, NULL);
+ } else if
+ (unlikely(!free_swap_and_cache(pte_to_swp_entry(ptent))))
+ print_bad_pte(vma, addr, ptent, NULL);
pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
} while (pte++, addr += PAGE_SIZE, (addr != end && *zap_work > 0));

@@ -2680,8 +2684,7 @@ static int do_nonlinear_fault(struct mm_
if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
return 0;

- if (unlikely(!(vma->vm_flags & VM_NONLINEAR) ||
- !(vma->vm_flags & VM_CAN_NONLINEAR))) {
+ if (unlikely(!(vma->vm_flags & VM_NONLINEAR))) {
/*
* Page table corrupted: show pte and kill process.
*/
--- badpage4/mm/swapfile.c 2008-11-28 20:37:16.000000000 +0000
+++ badpage5/mm/swapfile.c 2008-11-28 20:40:46.000000000 +0000
@@ -571,13 +571,13 @@ int try_to_free_swap(struct page *page)
* Free the swap entry like above, but also try to
* free the page cache entry if it is the last user.
*/
-void free_swap_and_cache(swp_entry_t entry)
+int free_swap_and_cache(swp_entry_t entry)
{
- struct swap_info_struct * p;
+ struct swap_info_struct *p;
struct page *page = NULL;

if (is_migration_entry(entry))
- return;
+ return 1;

p = swap_info_get(entry);
if (p) {
@@ -603,6 +603,7 @@ void free_swap_and_cache(swp_entry_t ent
unlock_page(page);
page_cache_release(page);
}
+ return p != NULL;
}

#ifdef CONFIG_HIBERNATION