Re: [RFC][PATCH] Avoid vmtruncate/mmap-page-fault race

[Paul E. McKenney]

On Thu, May 29, 2003 at 05:33:04PM +0100, Hugh Dickins wrote:
> On Thu, 29 May 2003, Paul E. McKenney wrote:
> > On Fri, May 23, 2003 at 11:42:02AM -0700, Paul E. McKenney wrote:
> > > 
> > > Exactly -- allows a ->nopage() to drop some lock to avoid races
> > > between pagefault and either vmtruncate() or invalidate_mmap_range().
> > > This race (from the cross-host mmap viewpoint) is described in:
> > > 
> > >     http://marc.theaimsgroup.com/?l=linux-kernel&m=105286345316249&w=2
> > 
> > Rediffed for 2.5.70-mm1.
> 
> Me?  I much preferred your original, much sparer, nopagedone patch
> (labelled "uglyh as hell" by hch).  I dislike passing lots of args
> down a level so they can be passed up again to the library function.
> 
> In particular, I feel queasy (fear loss of control) about passing a
> pmd_t* down to a filesystem, which I'd prefer to have no access to
> such.  But I may be in a minority, and the decision won't be mine.

Fine by me either way.  ;-)  Here is the rediffed nopagedone patch
for 2.5.70-mm1.

						Thanx, Paul

diff -urN -X dontdiff linux-2.5.70-mm1/include/linux/mm.h linux-2.5.70-mm1.nopagedone/include/linux/mm.h
--- linux-2.5.70-mm1/include/linux/mm.h	2003-05-28 20:16:04.000000000 -0700
+++ linux-2.5.70-mm1.nopagedone/include/linux/mm.h	2003-05-29 19:34:55.000000000 -0700
@@ -143,6 +143,7 @@
 	void (*open)(struct vm_area_struct * area);
 	void (*close)(struct vm_area_struct * area);
 	struct page * (*nopage)(struct vm_area_struct * area, unsigned long address, int unused);
+	void (*nopagedone)(struct vm_area_struct * area, unsigned long address, int status);
 	int (*populate)(struct vm_area_struct * area, unsigned long address, unsigned long len, pgprot_t prot, unsigned long pgoff, int nonblock);
 };
 
diff -urN -X dontdiff linux-2.5.70-mm1/mm/memory.c linux-2.5.70-mm1.nopagedone/mm/memory.c
--- linux-2.5.70-mm1/mm/memory.c	2003-05-28 20:16:04.000000000 -0700
+++ linux-2.5.70-mm1.nopagedone/mm/memory.c	2003-05-29 19:34:55.000000000 -0700
@@ -1468,6 +1468,9 @@
 	ret = VM_FAULT_OOM;
 out:
 	pte_chain_free(pte_chain);
+	if (vma->vm_ops && vma->vm_ops->nopagedone) {
+		vma->vm_ops->nopagedone(vma, address & PAGE_MASK, ret);
+	}
 	return ret;
 }