From patchwork Thu May 28 00:20:33 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Jerome Glisse X-Patchwork-Id: 11574077 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D9FDA739 for ; Thu, 28 May 2020 00:20:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C218F20888 for ; Thu, 28 May 2020 00:20:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LBCTMgjn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725385AbgE1AUv (ORCPT ); Wed, 27 May 2020 20:20:51 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:43035 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725681AbgE1AUu (ORCPT ); Wed, 27 May 2020 20:20:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1590625249; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=3NfM/YRWw8tWtCVntluiCugDqJX5J7Mi6y5RyulO5Co=; b=LBCTMgjny0ccH6a/443NcnWI+uWRzBBp3NDtVXmGbzg+B71vUpOu9Z/sKK5pbIXZnL7G3Y IrJaTyx75jI/ldMUILiEsB32ph1c1EFAPRAC/sfvqlUYx3jLfgGgGrcUNXVikfNcFiNcZa pKAsi9qzZ+CXWAWmt1i1rXXb5ldWAho= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-262--4PlExgtPwKJVseeIiuy9A-1; Wed, 27 May 2020 20:20:44 -0400 X-MC-Unique: -4PlExgtPwKJVseeIiuy9A-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D96EC460; Thu, 28 May 2020 00:20:40 +0000 (UTC) Received: from redhat.com (ovpn-119-19.rdu2.redhat.com [10.10.119.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2FCE85D9CC; Thu, 28 May 2020 00:20:35 +0000 (UTC) Date: Wed, 27 May 2020 20:20:33 -0400 From: Jerome Glisse To: linux-mm@kvack.org, Andrew Morton , Huang Ying Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Steven Capper , Catalin Marinas , Rabin Vincent , linux-arm-kernel@lists.infradead.org, rmk+kernel@arm.linux.org.uk, Guo Ren , linux-mips@vger.kernel.org, Ralf Baechle , Paul Burton , James Hogan , Ley Foon Tan , nios2-dev@lists.rocketboards.org, linux-parisc@vger.kernel.org, Helge Deller , "James E.J. Bottomley" , Yoshinori Sato , Rich Felker , linux-sh@vger.kernel.org, "David S. Miller" , sparclinux@vger.kernel.org, Guan Xuetao , linux-xtensa@linux-xtensa.org, Max Filippov , Chris Zankel Subject: Cache flush issue with page_mapping_file() and swap back shmem page ? Message-ID: <20200528002033.GB1992500@redhat.com> MIME-Version: 1.0 Content-Disposition: inline X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: linux-sh-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org So any arch code which uses page_mapping_file() might get the wrong answer, this function will return NULL for a swap backed page which can be a shmem pages. But shmem pages can still be shared among multiple process (and possibly at different virtual addresses if mremap was use). Attached is a patch that changes page_mapping_file() to return the shmem mapping for swap backed shmem page. I have not tested it (no way for me to test all those architecture) and i spotted this while working on something else. So i hope someone can take a closer look. Cheers, Jérôme From 6c76b9f8baa87ff872f6be5a44805a74c1e07fea Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= Date: Wed, 27 May 2020 20:18:59 -0400 Subject: [PATCH] mm: fix cache flush for shmem page that are swap backed. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This might be a shmem page that is in a sense a file that can be mapped multiple times in different processes at possibly different virtual addresses (fork + mremap). So return the shmem mapping that will allow any arch code to find all mappings of the page. Note that even if page is not anonymous then the page might have a NULL page->mapping field if it is being truncated, but then it is fine as each pte poiting to the page will be remove and cache flushing should be handled properly by that part of the code. Signed-off-by: Jérôme Glisse Cc: "Huang, Ying" Cc: Michal Hocko Cc: Mel Gorman Cc: Russell King Cc: Andrew Morton Cc: Mike Rapoport Cc: "David S. Miller" Cc: "James E.J. Bottomley" --- mm/util.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/mm/util.c b/mm/util.c index 988d11e6c17c..ec8739ab0cc3 100644 --- a/mm/util.c +++ b/mm/util.c @@ -685,8 +685,24 @@ EXPORT_SYMBOL(page_mapping); */ struct address_space *page_mapping_file(struct page *page) { - if (unlikely(PageSwapCache(page))) + if (unlikely(PageSwapCache(page))) { + /* + * This might be a shmem page that is in a sense a file that + * can be mapped multiple times in different processes at + * possibly different virtual addresses (fork + mremap). So + * return the shmem mapping that will allow any arch code to + * find all mappings of the page. + * + * Note that even if page is not anonymous then the page might + * have a NULL page->mapping field if it is being truncated, + * but then it is fine as each pte poiting to the page will be + * remove and cache flushing should be handled properly by that + * part of the code. + */ + if (!PageAnon(page)) + return page->mapping; return NULL; + } return page_mapping(page); }