From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f178.google.com (mail-ig0-f178.google.com [209.85.213.178]) by kanga.kvack.org (Postfix) with ESMTP id 01AEB6B0038 for ; Thu, 26 Nov 2015 03:02:28 -0500 (EST) Received: by igcto18 with SMTP id to18so6790338igc.0 for ; Thu, 26 Nov 2015 00:02:27 -0800 (PST) Received: from mail-io0-x22f.google.com (mail-io0-x22f.google.com. [2607:f8b0:4001:c06::22f]) by mx.google.com with ESMTPS id 21si26416469ioq.82.2015.11.26.00.02.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 26 Nov 2015 00:02:27 -0800 (PST) Received: by iouu10 with SMTP id u10so79297423iou.0 for ; Thu, 26 Nov 2015 00:02:27 -0800 (PST) From: 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org