On Mon, May 11, 2015 at 11:56:01AM +0530, Aneesh Kumar K.V wrote: > 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 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@xxxxxxxxxxxxxxx> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> CC: stable@ ? -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>