Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752699AbbKZICf (ORCPT ); Thu, 26 Nov 2015 03:02:35 -0500 Received: from mail-io0-f175.google.com ([209.85.223.175]:33442 "EHLO mail-io0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752486AbbKZIC2 (ORCPT ); Thu, 26 Nov 2015 03:02:28 -0500 From: Naoya Horiguchi To: Andrew Morton Cc: David Rientjes , Hugh Dickins , Dave Hansen , Mel Gorman , Joonsoo Kim , Hillf Danton , Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Naoya Horiguchi , Naoya Horiguchi Subject: [PATCH v1] mm: hugetlb: call huge_pte_alloc() only if ptep is null Date: Thu, 26 Nov 2015 17:02:16 +0900 Message-Id: <1448524936-10501-1-git-send-email-n-horiguchi@ah.jp.nec.com> X-Mailer: git-send-email 1.7.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1904 Lines: 49 Currently at the beginning of hugetlb_fault(), we call huge_pte_offset() and check whether the obtained *ptep is a migration/hwpoison entry or not. And if not, then we get to call huge_pte_alloc(). This is racy because the *ptep could turn into migration/hwpoison entry after the huge_pte_offset() check. This race results in BUG_ON in huge_pte_alloc(). We don't have to call huge_pte_alloc() when the huge_pte_offset() returns non-NULL, so let's fix this bug with moving the code into else block. Note that the *ptep could turn into a migration/hwpoison entry after this block, but that's not a problem because we have another !pte_present check later (we never go into hugetlb_no_page() in that case.) Fixes: 290408d4a250 ("hugetlb: hugepage migration core") Signed-off-by: Naoya Horiguchi Cc: [2.6.36+] --- mm/hugetlb.c | 8 ++++---- 1 files changed, 4 insertions(+), 4 deletions(-) diff --git next-20151123/mm/hugetlb.c next-20151123_patched/mm/hugetlb.c index 1101ccd..6ad5e91 100644 --- next-20151123/mm/hugetlb.c +++ next-20151123_patched/mm/hugetlb.c @@ -3696,12 +3696,12 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) return VM_FAULT_HWPOISON_LARGE | VM_FAULT_SET_HINDEX(hstate_index(h)); + } else { + ptep = huge_pte_alloc(mm, address, huge_page_size(h)); + if (!ptep) + return VM_FAULT_OOM; } - ptep = huge_pte_alloc(mm, address, huge_page_size(h)); - if (!ptep) - return VM_FAULT_OOM; - mapping = vma->vm_file->f_mapping; idx = vma_hugecache_offset(h, vma, address); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/