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.
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