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[PATCH] mm: pte_offset_map_lock loops

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Convert those common loops using page_table_lock on the outside and
pte_offset_map within to use just pte_offset_map_lock within instead.

These all hold mmap_sem (some exclusively, some not), so at no level can a
page table be whipped away from beneath them.  But whereas pte_alloc loops
tested with the "atomic" pmd_present, these loops are testing with pmd_none,
which on i386 PAE tests both lower and upper halves.

That's now unsafe, so add a cast into pmd_none to test only the vital lower
half: we lose a little sensitivity to a corrupt middle directory, but not
enough to worry about.  It appears that i386 and UML were the only
architectures vulnerable in this way, and pgd and pud no problem.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Hugh Dickins
2005-10-29 18:16:27 -07:00
committed by Linus Torvalds
parent 8f4e2101fd
commit 705e87c0c3
7 changed files with 30 additions and 47 deletions
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20
mm/swapfile.c
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@@ -401,8 +401,6 @@ void free_swap_and_cache(swp_entry_t entry)
* No need to decide whether this PTE shares the swap entry with others,
* 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.
*
* vma->vm_mm->page_table_lock is held.
*/
static void unuse_pte(struct vm_area_struct *vma, pte_t *pte,
unsigned long addr, swp_entry_t entry, struct page *page)
@@ -424,23 +422,25 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end,
swp_entry_t entry, struct page *page)
{
pte_t *pte;
pte_t swp_pte = swp_entry_to_pte(entry);
pte_t *pte;
spinlock_t *ptl;
int found = 0;
pte = pte_offset_map(pmd, addr);
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
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);
pte_unmap(pte);
return 1;
unuse_pte(vma, pte++, addr, entry, page);
found = 1;
break;
}
} while (pte++, addr += PAGE_SIZE, addr != end);
pte_unmap(pte - 1);
return 0;
pte_unmap_unlock(pte - 1, ptl);
return found;
}
static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
@@ -522,12 +522,10 @@ static int unuse_mm(struct mm_struct *mm,
down_read(&mm->mmap_sem);
lock_page(page);
}
spin_lock(&mm->page_table_lock);
for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (vma->anon_vma && unuse_vma(vma, entry, page))
break;
}
spin_unlock(&mm->page_table_lock);
up_read(&mm->mmap_sem);
/*
* Currently unuse_mm cannot fail, but leave error handling