linux-kernel - Re: [PATCH] mm: fix page_mkclean_one (was: 2.6.19 file content corruption on ext3)

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Date:	Wed, 20 Dec 2006 12:42:19 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jesper Juhl <jesper.juhl@...il.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Linus Torvalds <torvalds@...l.org>,
	Andrei Popa <andrei.popa@...eo.ro>,
	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hugh@...itas.com>,
	Florian Weimer <fw@...eb.enyo.de>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	Martin Michlmayr <tbm@...ius.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Arnd Bergmann <arnd.bergmann@...ibm.com>
Subject: Re: [PATCH] mm: fix page_mkclean_one (was: 2.6.19 file content
	corruption on ext3)

On Wed, 2006-12-20 at 12:39 +0100, Jesper Juhl wrote:
> On 20/12/06, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> >
> > fix page_mkclean_one()
> >
> > it had several issues:
> >  - it failed to flush the cache
> >  - it failed to flush the tlb
> >  - it failed to do s390 (s390 guys, please verify this is now correct)
> >
> > Also, clear in a loop to ensure SMP safeness as suggested by Arjan.
> >
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > ---
> >  mm/rmap.c |   29 +++++++++++++++--------------
> >  1 file changed, 15 insertions(+), 14 deletions(-)
> >
> > Index: linux-2.6/mm/rmap.c
> > ===================================================================
> > --- linux-2.6.orig/mm/rmap.c
> > +++ linux-2.6/mm/rmap.c
> > @@ -432,7 +432,7 @@ static int page_mkclean_one(struct page
> >  {
> >         struct mm_struct *mm = vma->vm_mm;
> >         unsigned long address;
> > -       pte_t *pte, entry;
> > +       pte_t *ptep;
> >         spinlock_t *ptl;
> >         int ret = 0;
> >
> > @@ -440,22 +440,23 @@ static int page_mkclean_one(struct page
> >         if (address == -EFAULT)
> >                 goto out;
> >
> > -       pte = page_check_address(page, mm, address, &ptl);
> > -       if (!pte)
> > +       ptep = page_check_address(page, mm, address, &ptl);
> > +       if (!ptep)
> >                 goto out;
> >
> > -       if (!pte_dirty(*pte) && !pte_write(*pte))
> > -               goto unlock;
> > -
> > -       entry = ptep_get_and_clear(mm, address, pte);
> > -       entry = pte_mkclean(entry);
> > -       entry = pte_wrprotect(entry);
> > -       ptep_establish(vma, address, pte, entry);
> > -       lazy_mmu_prot_update(entry);
> > -       ret = 1;
> > +       while (pte_dirty(*ptep) || pte_write(*ptep)) {
> > +               pte_t entry = ptep_get_and_clear(mm, address, ptep);
> > +               flush_cache_page(vma, address, pte_pfn(entry));
> > +               flush_tlb_page(vma, address);
> > +               (void)page_test_and_clear_dirty(page); /* do the s390 thing */
> > +               entry = pte_wrprotect(entry);
> > +               entry = pte_mkclean(entry);
> > +               set_pte_at(vma, address, ptep, entry);
> > +               lazy_mmu_prot_update(entry);
> > +               ret = 1;
> > +       }
> >
> Having the assignment of "ret = 1;" inside the loop seems a little
> pointless. Perhaps gcc can optimize it, but still, that assignment
> really only needs to happen once outside the loop.

Sure, but I was hoping gcc was smart enough. Placing it outside the loop
would require an extra if stmt. Also the chance this loop will actually
be traversed more than once is _very_ small.



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