On Monday 29 October 2007 23:35, Peter Zijlstra wrote:
> 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
I think it's a fine minimal patch. Maybe add a comment to say exactly
what we're doing here (pagecache generally just uses !mapping to test
for truncate).
Otherwise, Acked-by: Nick Piggin <[email protected]>, thanks!
> ---
> 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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