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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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