From: Hugh Dickins <hugh@veritas.com>
The get_user_pages force write case (from ptrace) expects that a single call
to handle_mm_fault is enough to give it a page it can safely write to. This
implies that when handling a write access to a page_mkwrite area, do_file_page
must now itself call do_wp_page to call page_mkwrite and (probably) make the
pte writable: that cannot safely be left to a subsequent fault.
Clarify today's flow of control in do_file_page: it is only called for a
pte_file entry, which only appears in a non-linear vma, which is always shared
and must have a populate: so the do_no_page path is never taken.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
mm/memory.c | 35 +++++++++++++++++++++++------------
1 files changed, 23 insertions(+), 12 deletions(-)
diff -puN mm/memory.c~fix-page-becoming-writable-in-do_file_page mm/memory.c
--- 25/mm/memory.c~fix-page-becoming-writable-in-do_file_page Wed Jul 13 14:21:34 2005
+++ 25-akpm/mm/memory.c Wed Jul 13 14:21:34 2005
@@ -1968,27 +1968,38 @@ static int do_file_page(struct mm_struct
unsigned long pgoff;
int err;
- BUG_ON(!vma->vm_ops || !vma->vm_ops->nopage);
- /*
- * Fall back to the linear mapping if the fs does not support
- * ->populate:
- */
- if (!vma->vm_ops || !vma->vm_ops->populate ||
- (write_access && !(vma->vm_flags & VM_SHARED))) {
- pte_clear(mm, address, pte);
- return do_no_page(mm, vma, address, write_access, pte, pmd);
- }
+ BUG_ON(!vma->vm_ops || !vma->vm_ops->populate);
+ BUG_ON(!(vma->vm_flags & VM_SHARED));
pgoff = pte_to_pgoff(*pte);
-
+again:
pte_unmap(pte);
spin_unlock(&mm->page_table_lock);
- err = vma->vm_ops->populate(vma, address & PAGE_MASK, PAGE_SIZE, vma->vm_page_prot, pgoff, 0);
+ err = vma->vm_ops->populate(vma, address & PAGE_MASK, PAGE_SIZE,
+ vma->vm_page_prot, pgoff, 0);
if (err == -ENOMEM)
return VM_FAULT_OOM;
if (err)
return VM_FAULT_SIGBUS;
+
+ /*
+ * For the get_user_pages force write case, we must make sure that
+ * page_mkwrite is called by this invocation of handle_mm_fault.
+ */
+ if (write_access && vma->vm_ops->page_mkwrite) {
+ pte_t entry;
+ int ret;
+
+ spin_lock(&mm->page_table_lock);
+ pte = pte_offset_map(pmd, address);
+ entry = *pte;
+ if (!pte_present(entry))
+ goto again;
+ ret = do_wp_page(mm, vma, address, pte, pmd, entry);
+ if (ret != VM_FAULT_MINOR)
+ return ret;
+ }
return VM_FAULT_MAJOR;
}
_