forked from Minki/linux
13bd817bb8
Serialize against find_linux_pte_or_hugepte() which does lock-less lookup in page tables with local interrupts disabled. For huge pages it casts pmd_t to pte_t. Since the format of pte_t is different from pmd_t we want to prevent transit from pmd pointing to page table to pmd pointing to huge page (and back) while interrupts are disabled. We clear pmd to possibly replace it with page table pointer in different code paths. So make sure we wait for the parallel find_linux_pte_or_hugepage() to finish. Without this patch, a find_linux_pte_or_hugepte() running in parallel to __split_huge_zero_page_pmd() or do_huge_pmd_wp_page_fallback() or zap_huge_pmd() can run into the above issue. With __split_huge_zero_page_pmd() and do_huge_pmd_wp_page_fallback() we clear the hugepage pte before inserting the pmd entry with a regular pgtable address. Such a clear need to wait for the parallel find_linux_pte_or_hugepte() to finish. With zap_huge_pmd(), we can run into issues, with a hugepage pte getting zapped due to a MADV_DONTNEED while other cpu fault it in as small pages. Reported-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
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