One of the side effects of speculating on faults (without holding mmap_sem) is that we can race with free_pgtables() and therefore we cannot assume the page-tables will stick around.
Remove the relyance on the pte pointer. Signed-off-by: Peter Zijlstra (Intel) <[email protected]> --- mm/memory.c | 76 ++++++++++++++++-------------------------------------------- 1 file changed, 21 insertions(+), 55 deletions(-) --- a/mm/memory.c +++ b/mm/memory.c @@ -1933,31 +1933,6 @@ int apply_to_page_range(struct mm_struct } EXPORT_SYMBOL_GPL(apply_to_page_range); -/* - * handle_pte_fault chooses page fault handler according to an entry - * which was read non-atomically. Before making any commitment, on - * those architectures or configurations (e.g. i386 with PAE) which - * might give a mix of unmatched parts, do_swap_page and do_nonlinear_fault - * must check under lock before unmapping the pte and proceeding - * (but do_wp_page is only called after already making such a check; - * and do_anonymous_page can safely check later on). - */ -static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd, - pte_t *page_table, pte_t orig_pte) -{ - int same = 1; -#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT) - if (sizeof(pte_t) > sizeof(unsigned long)) { - spinlock_t *ptl = pte_lockptr(mm, pmd); - spin_lock(ptl); - same = pte_same(*page_table, orig_pte); - spin_unlock(ptl); - } -#endif - pte_unmap(page_table); - return same; -} - static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma) { debug_dma_assert_idle(src); @@ -2407,21 +2382,18 @@ EXPORT_SYMBOL(unmap_mapping_range); * as does filemap_fault(). */ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long address, pte_t *page_table, pmd_t *pmd, + unsigned long address, pmd_t *pmd, unsigned int flags, pte_t orig_pte) { spinlock_t *ptl; struct page *page, *swapcache; struct mem_cgroup *memcg; swp_entry_t entry; - pte_t pte; + pte_t *page_table, pte; int locked; int exclusive = 0; int ret = 0; - if (!pte_unmap_same(mm, pmd, page_table, orig_pte)) - goto out; - entry = pte_to_swp_entry(orig_pte); if (unlikely(non_swap_entry(entry))) { if (is_migration_entry(entry)) { @@ -2624,15 +2596,13 @@ static inline int check_stack_guard_page * We return with mmap_sem still held, but pte unmapped and unlocked. */ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long address, pte_t *page_table, pmd_t *pmd, + unsigned long address, pmd_t *pmd, unsigned int flags) { struct mem_cgroup *memcg; struct page *page; spinlock_t *ptl; - pte_t entry; - - pte_unmap(page_table); + pte_t entry, *page_table; /* Check if we need to add a guard page to the stack */ if (check_stack_guard_page(vma, address) < 0) @@ -3031,13 +3001,12 @@ static int do_shared_fault(struct mm_str * return value. See filemap_fault() and __lock_page_or_retry(). */ static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long address, pte_t *page_table, pmd_t *pmd, + unsigned long address, pmd_t *pmd, unsigned int flags, pte_t orig_pte) { pgoff_t pgoff = (((address & PAGE_MASK) - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; - pte_unmap(page_table); if (!(flags & FAULT_FLAG_WRITE)) return do_read_fault(mm, vma, address, pmd, pgoff, flags, orig_pte); @@ -3059,16 +3028,13 @@ static int do_linear_fault(struct mm_str * return value. See filemap_fault() and __lock_page_or_retry(). */ static int do_nonlinear_fault(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long address, pte_t *page_table, pmd_t *pmd, + unsigned long address, pmd_t *pmd, unsigned int flags, pte_t orig_pte) { pgoff_t pgoff; flags |= FAULT_FLAG_NONLINEAR; - if (!pte_unmap_same(mm, pmd, page_table, orig_pte)) - return 0; - if (unlikely(!(vma->vm_flags & VM_NONLINEAR))) { /* * Page table corrupted: show pte and kill process. @@ -3103,7 +3069,7 @@ static int numa_migrate_prep(struct page } static int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long addr, pte_t pte, pte_t *ptep, pmd_t *pmd) + unsigned long addr, pte_t pte, pmd_t *pmd) { struct page *page = NULL; spinlock_t *ptl; @@ -3112,6 +3078,7 @@ static int do_numa_page(struct mm_struct int target_nid; bool migrated = false; int flags = 0; + pte_t *ptep; /* * The "pte" at this point cannot be used safely without @@ -3122,8 +3089,7 @@ static int do_numa_page(struct mm_struct * the _PAGE_NUMA bit and it is not really expected that there * would be concurrent hardware modifications to the PTE. */ - ptl = pte_lockptr(mm, pmd); - spin_lock(ptl); + ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); if (unlikely(!pte_same(*ptep, pte))) { pte_unmap_unlock(ptep, ptl); goto out; @@ -3195,34 +3161,32 @@ static int do_numa_page(struct mm_struct */ static int handle_pte_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, - pte_t *pte, pmd_t *pmd, unsigned int flags) + pte_t entry, pmd_t *pmd, unsigned int flags) { - pte_t entry; spinlock_t *ptl; + pte_t *pte; - entry = ACCESS_ONCE(*pte); if (!pte_present(entry)) { if (pte_none(entry)) { if (vma->vm_ops) { if (likely(vma->vm_ops->fault)) return do_linear_fault(mm, vma, address, - pte, pmd, flags, entry); + pmd, flags, entry); } return do_anonymous_page(mm, vma, address, - pte, pmd, flags); + pmd, flags); } if (pte_file(entry)) return do_nonlinear_fault(mm, vma, address, - pte, pmd, flags, entry); + pmd, flags, entry); return do_swap_page(mm, vma, address, - pte, pmd, flags, entry); + pmd, flags, entry); } if (pte_numa(entry)) - return do_numa_page(mm, vma, address, entry, pte, pmd); + return do_numa_page(mm, vma, address, entry, pmd); - ptl = pte_lockptr(mm, pmd); - spin_lock(ptl); + pte = pte_offset_map_lock(mm, pmd, address, &ptl); if (unlikely(!pte_same(*pte, entry))) goto unlock; if (flags & FAULT_FLAG_WRITE) { @@ -3261,7 +3225,7 @@ static int __handle_mm_fault(struct mm_s pgd_t *pgd; pud_t *pud; pmd_t *pmd; - pte_t *pte; + pte_t *pte, entry; if (unlikely(is_vm_hugetlb_page(vma))) return hugetlb_fault(mm, vma, address, flags); @@ -3331,8 +3295,10 @@ static int __handle_mm_fault(struct mm_s * safe to run pte_offset_map(). */ pte = pte_offset_map(pmd, address); + entry = ACCESS_ONCE(*pte); + pte_unmap(pte); - return handle_pte_fault(mm, vma, address, pte, pmd, flags); + return handle_pte_fault(mm, vma, address, entry, pmd, flags); } /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
