On Mon, 2007-10-29 at 11:11 +0100, Peter Zijlstra wrote:
> On Mon, 2007-10-29 at 01:17 -0700, Jaya Kumar wrote:
> > On 10/29/07, Andrew Morton <[email protected]> wrote:
> > > On Mon, 22 Oct 2007 16:40:57 +0200 Stefani Seibold <[email protected]> wrote:
> > > >
> > > > The problem original occurs with the fb_defio driver (driver/video/fb_defio.c).
> > > > This driver use the vm_ops.page_mkwrite() handler for tracking the modified pages,
> > > > which will be in an extra thread handled, to perform the IO and clean and
> > > > write protect all pages with page_clean().
> > > >
> >
> > Hi,
> >
> > An aside, I just tested that deferred IO works fine on 2.6.22.10/pxa255.
> >
> > I understood from the thread that PeterZ is looking into page_mkclean
> > changes which I guess went into 2.6.23. I'm also happy to help in any
> > way if the way we're doing fb_defio needs to change.
>
> Yeah, its the truncate race stuff introduced by Nick in
> d0217ac04ca6591841e5665f518e38064f4e65bd
>
> I'm a bit at a loss on how to go around fixing this. One ugly idea I had
> was to check page->mapping before going into page_mkwrite() and when
> that is null, don't bother with the truncate check.
Something like this
---
mm/memory.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c
+++ linux-2.6/mm/memory.c
@@ -2300,6 +2300,8 @@ static int __do_fault(struct mm_struct *
* to become writable
*/
if (vma->vm_ops->page_mkwrite) {
+ struct address_space *mapping = page->mapping;
+
unlock_page(page);
if (vma->vm_ops->page_mkwrite(vma, page) < 0) {
ret = VM_FAULT_SIGBUS;
@@ -2314,7 +2316,7 @@ static int __do_fault(struct mm_struct *
* reworking page_mkwrite locking API, which
* is better done later.
*/
- if (!page->mapping) {
+ if (mapping != page->mapping) {
ret = 0;
anon = 1; /* no anon but release vmf.page */
goto out;
-
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