"Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> writes: > 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@ ? Yes, We also need to pick, dac5657067919161eb3273ca787d8ae9814801e7 691e95fd7396905a38d98919e9c150dbc3ea21a3 7d6e7f7ffaba4e013c7a0589140431799bc17985 But that may need me to a backport, because we have dependencies in kvm and a cherry-pick may not work. Will work with Michael Ellerman to find out what needs to be done. -aneesh -- 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>