From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ie0-f174.google.com (mail-ie0-f174.google.com [209.85.223.174]) by kanga.kvack.org (Postfix) with ESMTP id 26FB16B005C for ; Fri, 1 Aug 2014 17:54:01 -0400 (EDT) Received: by mail-ie0-f174.google.com with SMTP id rp18so6788693iec.19 for ; Fri, 01 Aug 2014 14:54:00 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id ie1si25314203icb.43.2014.08.01.14.54.00 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 01 Aug 2014 14:54:00 -0700 (PDT) Date: Fri, 1 Aug 2014 14:53:58 -0700 From: Andrew Morton Subject: Re: [PATCH v2 1/3] mm/hugetlb: take refcount under page table lock in follow_huge_pmd() Message-Id: <20140801145358.0d673fc05235d941ca9dec0e@linux-foundation.org> In-Reply-To: <1406914663-8631-1-git-send-email-n-horiguchi@ah.jp.nec.com> References: <1406914663-8631-1-git-send-email-n-horiguchi@ah.jp.nec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Hugh Dickins , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Naoya Horiguchi On Fri, 1 Aug 2014 13:37:41 -0400 Naoya Horiguchi wrote: > We have a race condition between move_pages() and freeing hugepages, > where move_pages() calls follow_page(FOLL_GET) for hugepages internally > and tries to get its refcount without preventing concurrent freeing. > This race crashes the kernel, so this patch fixes it by moving FOLL_GET > code for hugepages into follow_huge_pmd() with taking the page table lock. > > This patch passes the following test. And libhugetlbfs test shows no > regression. > > ... How were these bugs discovered? Are we missing some Reported-by's? > --- mmotm-2014-07-22-15-58.orig/include/linux/hugetlb.h > +++ mmotm-2014-07-22-15-58/include/linux/hugetlb.h > @@ -101,6 +101,8 @@ struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address, > pmd_t *pmd, int write); > struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address, > pud_t *pud, int write); > +struct page *follow_huge_pmd_lock(struct vm_area_struct *vma, > + unsigned long address, pmd_t *pmd, int flags); > int pmd_huge(pmd_t pmd); > int pud_huge(pud_t pmd); > unsigned long hugetlb_change_protection(struct vm_area_struct *vma, > > ... > > --- mmotm-2014-07-22-15-58.orig/mm/hugetlb.c > +++ mmotm-2014-07-22-15-58/mm/hugetlb.c > @@ -3687,6 +3687,33 @@ follow_huge_pud(struct mm_struct *mm, unsigned long address, > > #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */ > > +struct page *follow_huge_pmd_lock(struct vm_area_struct *vma, > + unsigned long address, pmd_t *pmd, int flags) Some documentation here wouldn't hurt. Why it exists, what it does. And especially: any preconditions to calling it (ie: locking). > +{ > + struct page *page; > + spinlock_t *ptl; > + > + if (flags & FOLL_GET) > + ptl = huge_pte_lock(hstate_vma(vma), vma->vm_mm, (pte_t *)pmd); > + > + page = follow_huge_pmd(vma->vm_mm, address, pmd, flags & FOLL_WRITE); > + > + if (flags & FOLL_GET) { > + /* > + * Refcount on tail pages are not well-defined and > + * shouldn't be taken. The caller should handle a NULL > + * return when trying to follow tail pages. > + */ > + if (PageHead(page)) > + get_page(page); > + else > + page = NULL; > + spin_unlock(ptl); > + } > + > + return page; > +} > + > #ifdef CONFIG_MEMORY_FAILURE I can't find an implementation of follow_huge_pmd() which actually uses the fourth argument "write". Zap? Ditto for follow_huge_pud(). -- 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