From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f177.google.com (mail-io0-f177.google.com [209.85.223.177]) by kanga.kvack.org (Postfix) with ESMTP id 9ADBF6B0038 for ; Thu, 26 Nov 2015 03:29:51 -0500 (EST) Received: by ioir85 with SMTP id r85so79516110ioi.1 for ; Thu, 26 Nov 2015 00:29:51 -0800 (PST) Received: from us-alimail-mta2.hst.scl.en.alidc.net (mail113-251.mail.alibaba.com. [205.204.113.251]) by mx.google.com with ESMTP id wf4si2817545pab.231.2015.11.26.00.29.48 for ; Thu, 26 Nov 2015 00:29:50 -0800 (PST) Reply-To: "Hillf Danton" From: "Hillf Danton" References: <1448524936-10501-1-git-send-email-n-horiguchi@ah.jp.nec.com> In-Reply-To: <1448524936-10501-1-git-send-email-n-horiguchi@ah.jp.nec.com> Subject: Re: [PATCH v1] mm: hugetlb: call huge_pte_alloc() only if ptep is null Date: Thu, 26 Nov 2015 16:29:30 +0800 Message-ID: <00d301d12824$932eda30$b98c8e90$@alibaba-inc.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Content-Language: zh-cn Sender: owner-linux-mm@kvack.org List-ID: To: 'Naoya Horiguchi' , 'Andrew Morton' Cc: 'David Rientjes' , 'Hugh Dickins' , 'Dave Hansen' , 'Mel Gorman' , 'Joonsoo Kim' , 'Mike Kravetz' , linux-mm@kvack.org, linux-kernel@vger.kernel.org, '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+] > --- Acked-by: Hillf Danton > 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