From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 973AFFC6197 for ; Fri, 8 Nov 2019 09:38:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 78F0A21D7E for ; Fri, 8 Nov 2019 09:38:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730623AbfKHJij (ORCPT ); Fri, 8 Nov 2019 04:38:39 -0500 Received: from mx2.suse.de ([195.135.220.15]:39772 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1731444AbfKHJi2 (ORCPT ); Fri, 8 Nov 2019 04:38:28 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 0B306AE8A; Fri, 8 Nov 2019 09:38:24 +0000 (UTC) From: Vlastimil Babka To: stable@vger.kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ajay Kaher , Will Deacon , Punit Agrawal , Steve Capper , "Kirill A . Shutemov" , "Aneesh Kumar K . V" , Catalin Marinas , Naoya Horiguchi , Mark Rutland , Hillf Danton , Michal Hocko , Mike Kravetz , Andrew Morton , Linus Torvalds , Vlastimil Babka Subject: [PATCH STABLE 4.4 1/8] mm, gup: remove broken VM_BUG_ON_PAGE compound check for hugepages Date: Fri, 8 Nov 2019 10:38:07 +0100 Message-Id: <20191108093814.16032-2-vbabka@suse.cz> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191108093814.16032-1-vbabka@suse.cz> References: <20191108093814.16032-1-vbabka@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Will Deacon commit a3e328556d41bb61c55f9dfcc62d6a826ea97b85 upstream. When operating on hugepages with DEBUG_VM enabled, the GUP code checks the compound head for each tail page prior to calling page_cache_add_speculative. This is broken, because on the fast-GUP path (where we don't hold any page table locks) we can be racing with a concurrent invocation of split_huge_page_to_list. split_huge_page_to_list deals with this race by using page_ref_freeze to freeze the page and force concurrent GUPs to fail whilst the component pages are modified. This modification includes clearing the compound_head field for the tail pages, so checking this prior to a successful call to page_cache_add_speculative can lead to false positives: In fact, page_cache_add_speculative *already* has this check once the page refcount has been successfully updated, so we can simply remove the broken calls to VM_BUG_ON_PAGE. Link: http://lkml.kernel.org/r/20170522133604.11392-2-punit.agrawal@arm.com Signed-off-by: Will Deacon Signed-off-by: Punit Agrawal Acked-by: Steve Capper Acked-by: Kirill A. Shutemov Cc: Aneesh Kumar K.V Cc: Catalin Marinas Cc: Naoya Horiguchi Cc: Mark Rutland Cc: Hillf Danton Cc: Michal Hocko Cc: Mike Kravetz Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Vlastimil Babka --- mm/gup.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 2cd3b31e3666..6f9088cb8ebe 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1134,7 +1134,6 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); tail = page; do { - VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; page++; @@ -1181,7 +1180,6 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); tail = page; do { - VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; page++; @@ -1224,7 +1222,6 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT); tail = page; do { - VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; page++; -- 2.23.0