From: Hugh Dickins hughd@google.com Subject: khugepaged: collapse_pte_mapped_thp() flush the right range
pmdp_collapse_flush() should be given the start address at which the huge page is mapped, haddr: it was given addr, which at that point has been used as a local variable, incremented to the end address of the extent.
Found by source inspection while chasing a hugepage locking bug, which I then could not explain by this. At first I thought this was very bad; then saw that all of the page translations that were not flushed would actually still point to the right pages afterwards, so harmless; then realized that I know nothing of how different architectures and models cache intermediate paging structures, so maybe it matters after all - particularly since the page table concerned is immediately freed.
Much easier to fix than to think about.
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008021204390.27773@eggly.anvils Fixes: 27e1f8273113 ("khugepaged: enable collapse pmd for pte-mapped THP") Signed-off-by: Hugh Dickins hughd@google.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Song Liu songliubraving@fb.com Cc: stable@vger.kernel.org [5.4+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/khugepaged.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/khugepaged.c~khugepaged-collapse_pte_mapped_thp-flush-the-right-range +++ a/mm/khugepaged.c @@ -1502,7 +1502,7 @@ void collapse_pte_mapped_thp(struct mm_s
/* step 4: collapse pmd */ ptl = pmd_lock(vma->vm_mm, pmd); - _pmd = pmdp_collapse_flush(vma, addr, pmd); + _pmd = pmdp_collapse_flush(vma, haddr, pmd); spin_unlock(ptl); mm_dec_nr_ptes(mm); pte_free(mm, pmd_pgtable(_pmd)); _