On Wed, Mar 07, 2007 at 03:34:00AM -0800, Andrew Morton wrote:
> On Wed, 7 Mar 2007 03:20:38 -0800 Andrew Morton <[EMAIL PROTECTED]> wrote:
>
> >
> > > ===================================================================
> > > --- linux-2.6.orig/mm/memory.c
> > > +++ linux-2.6/mm/memory.c
> > > @@ -1676,6 +1676,17 @@ gotten:
> > > unlock:
> > > pte_unmap_unlock(page_table, ptl);
> > > if (dirty_page) {
> > > + /*
> > > + * Yes, Virginia, this is actually required to prevent a race
> > > + * with clear_page_dirty_for_io() from clearing the page dirty
> > > + * bit after it clear all dirty ptes, but before a racing
> > > + * do_wp_page installs a dirty pte.
> > > + *
> > > + * do_fault is protected similarly by holding the page lock
> > > + * after the dirty pte is installed.
> > > + */
> > > + lock_page(dirty_page);
> > > + unlock_page(dirty_page);
> > > set_page_dirty_balance(dirty_page);
> > > put_page(dirty_page);
> >
> > Yes, I think that'll plug it. A wait_on_page_locked() should suffice.
>
> Or will it? Suppose after the unlock_page() a _second_
> clear_page_dirty_for_io() gets run - the same thing happens?
>
> Extending the lock_page() coverage around the set_page_dirty() would
> prevent that.
>
> I guess not needed - the second clear_page_dirty_for_io() will have cleaned
> the
> pte.
Yeah, all we need to do is keep page faults out of that little window
in clear_page_dirty_for_io() where I stuck the comment.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
