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SubjectRe: [PATCH] mm: fix page_mkclean_one (was: 2.6.19 file content corruption on ext3)
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On Wed, 2006-12-20 at 12:39 +0100, Jesper Juhl wrote:
> On 20/12/06, Peter Zijlstra <a.p.zijlstra@chello.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@chello.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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