From patchwork Fri Aug 2 19:29:56 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vivek Goyal X-Patchwork-Id: 11074063 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 435A413AC for ; Fri, 2 Aug 2019 19:30:02 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 317E628864 for ; Fri, 2 Aug 2019 19:30:02 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 21E45288AF; Fri, 2 Aug 2019 19:30:02 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.1 Received: from ml01.01.org (ml01.01.org [198.145.21.10]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id CB1DD28864 for ; Fri, 2 Aug 2019 19:30:01 +0000 (UTC) Received: from [127.0.0.1] (localhost [IPv6:::1]) by ml01.01.org (Postfix) with ESMTP id E363B21309DB4; Fri, 2 Aug 2019 12:32:31 -0700 (PDT) X-Original-To: linux-nvdimm@lists.01.org Delivered-To: linux-nvdimm@lists.01.org Received-SPF: Pass (sender SPF authorized) identity=mailfrom; client-ip=209.132.183.28; helo=mx1.redhat.com; envelope-from=vgoyal@redhat.com; receiver=linux-nvdimm@lists.01.org Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id D0539213030AE for ; Fri, 2 Aug 2019 12:32:30 -0700 (PDT) Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 089EF3CA12; Fri, 2 Aug 2019 19:29:59 +0000 (UTC) Received: from horse.redhat.com (unknown [10.18.25.158]) by smtp.corp.redhat.com (Postfix) with ESMTP id A4D4F19C68; Fri, 2 Aug 2019 19:29:56 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 2C27C22377E; Fri, 2 Aug 2019 15:29:56 -0400 (EDT) Date: Fri, 2 Aug 2019 15:29:56 -0400 From: Vivek Goyal To: dan.j.williams@intel.com, linux-nvdimm@lists.01.org Subject: [PATCH] dax: dax_layout_busy_page() should not unmap cow pages Message-ID: <20190802192956.GA3032@redhat.com> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 02 Aug 2019 19:29:59 +0000 (UTC) X-BeenThere: linux-nvdimm@lists.01.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Linux-nvdimm developer list." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-fsdevel@vger.kernel.org, virtio-fs@redhat.com Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" X-Virus-Scanned: ClamAV using ClamSMTP As of now dax_layout_busy_page() calls unmap_mapping_range() with last argument as 1, which says even unmap cow pages. I am wondering who needs to get rid of cow pages as well. I noticed one interesting side affect of this. I mount xfs with -o dax and mmaped a file with MAP_PRIVATE and wrote some data to a page which created cow page. Then I called fallocate() on that file to zero a page of file. fallocate() called dax_layout_busy_page() which unmapped cow pages as well and then I tried to read back the data I wrote and what I get is old data from persistent memory. I lost the data I had written. This read basically resulted in new fault and read back the data from persistent memory. This sounds wrong. Are there any users which need to unmap cow pages as well? If not, I am proposing changing it to not unmap cow pages. I noticed this while while writing virtio_fs code where when I tried to reclaim a memory range and that corrupted the executable and I was running from virtio-fs and program got segment violation. Signed-off-by: Vivek Goyal --- fs/dax.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: rhvgoyal-linux/fs/dax.c =================================================================== --- rhvgoyal-linux.orig/fs/dax.c 2019-08-01 17:03:10.574675652 -0400 +++ rhvgoyal-linux/fs/dax.c 2019-08-02 14:32:28.809639116 -0400 @@ -600,7 +600,7 @@ struct page *dax_layout_busy_page(struct * guaranteed to either see new references or prevent new * references from being established. */ - unmap_mapping_range(mapping, 0, 0, 1); + unmap_mapping_range(mapping, 0, 0, 0); xas_lock_irq(&xas); xas_for_each(&xas, entry, ULONG_MAX) {