Re: [PATCH]: ufs: ufs_get_locked_patch race fix

Andrew Morton
2006-08-01T07:40:09Z

On Tue, 1 Aug 2006 11:30:43 +0400
Evgeniy Dushistov <dushistov@mail.ru> wrote:

> On Mon, Jul 31, 2006 at 11:02:51PM -0700, Andrew Morton wrote:
> > On Mon, 31 Jul 2006 16:57:02 +0400
> > Evgeniy Dushistov <dushistov@mail.ru> wrote:
> >
> > Looks good to me.
> >
> > Is there any need to be checking ->index? Normally we simply use the
> > sequence:
> >
> > lock_page(page);
> > if (page->mapping == NULL)
> > /* truncate got there first */
> >
> > to handle this case.
>
> Yes, I made it in analogy with `find_lock_page' and missed fact
> that if we increment usage counter of page, we have no need to check
> page->index.

OK. find_lock_page() has the splice stuff in it.

> Need another patch?

Is OK, I updated it.

I'm not sure that the `goto repeat' is needed if truncate got there first,
really - if truncate took the page down then it's now outside i_size and
shouldn't be coming back.

If the page _can_ come back then this code is all rather problematic.
Because this means that the page can come back (via an extending write())
one nanosecond after ufs_get_locked_page() returns NULL. Won't the callers
of ufs_get_locked_page() get confused by that?