Re: Race between vmtruncate and mapped areas?

[Andrew Morton]

Andrea Arcangeli <[e-mail]> wrote:
>
>  what do you think of this untested fix?
> 
>  I wonder if vm_file is valid for all nopage operations, I think it
>  should, and the i_mapping as well should always exist, but in the worst
>  case it shouldn't be too difficult to take care of special cases
>  (just checking if the new_page is reserved and if the vma is VM_SPECIAL)
>  would eliminate most issues, shall there be any.

yes, I think this is a good solution.

In 2.5 (at least) we can push all the sequence number work into
filemap_nopage(), and add a new vm_ops->revalidate() thing, so do_no_page()
doesn't need to know about inodes and such.

So the mm/memory.c part would look something like:

diff -puN mm/memory.c~a mm/memory.c
--- 25/mm/memory.c~a	2003-05-15 01:29:21.000000000 -0700
+++ 25-akpm/mm/memory.c	2003-05-15 01:32:02.000000000 -0700
@@ -1399,7 +1399,7 @@ do_no_page(struct mm_struct *mm, struct 
 					pmd, write_access, address);
 	pte_unmap(page_table);
 	spin_unlock(&mm->page_table_lock);
-
+retry:
 	new_page = vma->vm_ops->nopage(vma, address & PAGE_MASK, 0);
 
 	/* no page was available -- either SIGBUS or OOM */
@@ -1408,9 +1408,11 @@ do_no_page(struct mm_struct *mm, struct 
 	if (new_page == NOPAGE_OOM)
 		return VM_FAULT_OOM;
 
-	pte_chain = pte_chain_alloc(GFP_KERNEL);
-	if (!pte_chain)
-		goto oom;
+	if (!pte_chain) {
+		pte_chain = pte_chain_alloc(GFP_KERNEL);
+		if (!pte_chain)
+			goto oom;
+	}
 
 	/*
 	 * Should we do an early C-O-W break?
@@ -1428,6 +1430,17 @@ do_no_page(struct mm_struct *mm, struct 
 	}
 
 	spin_lock(&mm->page_table_lock);
+
+	/*
+	 * comment goes here
+	 */
+	if (vma->vm_ops && vma->vm_ops->revalidate &&
+			vma->vm_ops->revalidate(vma, address) {
+		spin_unlock(&mm->page_table_lock);
+		put_page(new_page);
+		goto retry;
+	}
+
 	page_table = pte_offset_map(pmd, address);
 
 	/*

_