mm: fix page table unmap for stack guard page properly

[net-next-2.6.git] / mm / memory.c

diff --git a/mm/memory.c b/mm/memory.c
index 858829d06a924291190c159614bd7f9dbbf374d1..b6e5fd23cc5a48e13f49b0d824ca3cc9713bd3ab 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2759,6 +2759,26 @@ out_release:
        return ret;
 }
 
+/*
+ * This is like a special single-page "expand_downwards()",
+ * except we must first make sure that 'address-PAGE_SIZE'
+ * doesn't hit another vma.
+ *
+ * The "find_vma()" will do the right thing even if we wrap
+ */
+static inline int check_stack_guard_page(struct vm_area_struct *vma, unsigned long address)
+{
+       address &= PAGE_MASK;
+       if ((vma->vm_flags & VM_GROWSDOWN) && address == vma->vm_start) {
+               address -= PAGE_SIZE;
+               if (find_vma(vma->vm_mm, address) != vma)
+                       return -ENOMEM;
+
+               expand_stack(vma, address);
+       }
+       return 0;
+}
+
 /*
  * We enter with non-exclusive mmap_sem (to exclude vma changes,
  * but allow concurrent faults), and pte mapped but not yet locked.
@@ -2772,19 +2792,23 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
        spinlock_t *ptl;
        pte_t entry;
 
+       pte_unmap(page_table);
+
+       /* Check if we need to add a guard page to the stack */
+       if (check_stack_guard_page(vma, address) < 0)
+               return VM_FAULT_SIGBUS;
+
+       /* Use the zero-page for reads */
        if (!(flags & FAULT_FLAG_WRITE)) {
                entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
                                                vma->vm_page_prot));
-               ptl = pte_lockptr(mm, pmd);
-               spin_lock(ptl);
+               page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
                if (!pte_none(*page_table))
                        goto unlock;
                goto setpte;
        }
 
        /* Allocate our own private page. */
-       pte_unmap(page_table);
-
        if (unlikely(anon_vma_prepare(vma)))
                goto oom;
        page = alloc_zeroed_user_highpage_movable(vma, address);