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Subject[PATCH 2.5.66-mm2] Fix page_convert_anon locking issues

I came up with a scheme for accessing the page tables in page_convert_anon
that should work without requiring locks. Hugh has looked at it and agrees
it addresses the problems he found. Anyway, here's the patch.

Dave McCracken

======================================================================
Dave McCracken IBM Linux Base Kernel Team 1-512-838-3059
dmccr@us.ibm.com T/L 678-3059
--- 2.5.66-mm2/./mm/rmap.c 2003-04-01 11:23:35.000000000 -0600
+++ 2.5.66-mm2-fix/./mm/rmap.c 2003-04-01 11:30:21.000000000 -0600
@@ -95,7 +95,9 @@ find_pte(struct vm_area_struct *vma, str
{
struct mm_struct *mm = vma->vm_mm;
pgd_t *pgd;
+ pgd_t pgdval;
pmd_t *pmd;
+ pmd_t pmdval;
pte_t *pte;
unsigned long loffset;
unsigned long address;
@@ -106,17 +108,27 @@ find_pte(struct vm_area_struct *vma, str
goto out;

pgd = pgd_offset(mm, address);
- if (!pgd_present(*pgd))
+ pgdval = *pgd;
+ if (!pgd_present(pgdval))
goto out;

- pmd = pmd_offset(pgd, address);
- if (!pmd_present(*pmd))
+ pmd = pmd_offset(&pgdval, address);
+ pmdval = *pmd;
+ if (!pmd_present(pmdval))
goto out;

- pte = pte_offset_map(pmd, address);
+ /* Double check to make sure the pmd page hasn't been freed */
+ if (!pgd_present(*pgd))
+ goto out;
+
+ pte = pte_offset_map(&pmdval, address);
if (!pte_present(*pte))
goto out_unmap;

+ /* Double check to make sure the pte page hasn't been freed */
+ if (!pmd_present(*pmd))
+ goto out_unmap;
+
if (page_to_pfn(page) != pte_pfn(*pte))
goto out_unmap;
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