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SubjectRe: [PATCH linux-2.6.0-test10-mm1] filemap_fdatawait.patch
Suparna Bhattacharya <suparna@in.ibm.com> wrote:
>
> On Wed, Dec 31, 2003 at 03:17:36AM -0800, Andrew Morton wrote:
> > Andrew Morton <akpm@osdl.org> wrote:
> > >
> > > Let me actually think about this a bit.
> >
> > Nasty. The same race is present in 2.4.x...
> >
> > How's about we start new I/O in filemap_fdatawait() if the page is dirty?
> >
>
> Makes sense to me.
> There's a chance that this could explain why Daniel saw exposures even
> with his fix.
>
> Would be interesting to see his results with your patch.
>
> Though we might as well plug this anyway ?

Yes, we should. I'm not dreadfully keen on starting I/O from within
filemap_fdatawait() though - it seems "wrong" somehow.

> >
> > diff -puN mm/filemap.c~a mm/filemap.c
> > --- 25/mm/filemap.c~a 2003-12-31 03:10:29.000000000 -0800
> > +++ 25-akpm/mm/filemap.c 2003-12-31 03:17:05.000000000 -0800
> > @@ -206,7 +206,13 @@ restart:
> > page_cache_get(page);
> > spin_unlock(&mapping->page_lock);
> >
> > - wait_on_page_writeback(page);
> > + lock_page(page);
> > + if (PageDirty(page) && mapping->a_ops->writepage) {
> > + write_one_page(page, 1);
> > + } else {
> > + wait_on_page_writeback(page);
> > + unlock_page(page);
>
> Would we lose anything if we unlock_page() before wait_on_page_writeback() ?

No, that should be OK.


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