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=-3.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 DCA3AC432C0 for ; Fri, 22 Nov 2019 16:08:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B20C52071B for ; Fri, 22 Nov 2019 16:08:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="PPcd75AM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727020AbfKVQIz (ORCPT ); Fri, 22 Nov 2019 11:08:55 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:57816 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726546AbfKVQIz (ORCPT ); Fri, 22 Nov 2019 11:08:55 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574438934; 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: in-reply-to:in-reply-to:references:references; bh=aChokPuSf/E1/myJnN2scacEgSwoRMHnNtyJ+8WYM+U=; b=PPcd75AMJjannlJf7Bcq4CKSt/4O0/Tio3udOIxTQ9TFlE5W3pLXAr+xqKuB0seprqMJwj CF9BuiN+LlAnYkJSrI50Hgghrg+7BICQbagYV5/AmdqX2CYsJFcQz2FSQi2GY3XQVmO7x8 AOI/ISOeTVfVZ4D5r1lBEg/jV9wumvc= 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-179-paFjoYLyMj6EbrgB8Ql3JA-1; Fri, 22 Nov 2019 11:08:51 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 889F01005510; Fri, 22 Nov 2019 16:08:49 +0000 (UTC) Received: from segfault.boston.devel.redhat.com (segfault.boston.devel.redhat.com [10.19.60.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2B08A8516; Fri, 22 Nov 2019 16:08:48 +0000 (UTC) From: Jeff Moyer To: Dan Williams Cc: Pankaj Gupta , linux-nvdimm , Linux Kernel Mailing List , Linux ACPI , Vishal L Verma , Dave Jiang , "Weiny\, Ira" , "Rafael J. Wysocki" , Len Brown , Vivek Goyal , Keith Busch Subject: Re: [PATCH] virtio pmem: fix async flush ordering References: <20191120092831.6198-1-pagupta@redhat.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 Date: Fri, 22 Nov 2019 11:08:46 -0500 In-Reply-To: (Dan Williams's message of "Wed, 20 Nov 2019 23:23:46 -0800") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-MC-Unique: paFjoYLyMj6EbrgB8Ql3JA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dan Williams writes: > On Wed, Nov 20, 2019 at 9:26 AM Jeff Moyer wrote: >> >> Pankaj Gupta writes: >> >> > Remove logic to create child bio in the async flush function which >> > causes child bio to get executed after parent bio 'pmem_make_request' >> > completes. This resulted in wrong ordering of REQ_PREFLUSH with the >> > data write request. >> > >> > Instead we are performing flush from the parent bio to maintain the >> > correct order. Also, returning from function 'pmem_make_request' if >> > REQ_PREFLUSH returns an error. >> > >> > Reported-by: Jeff Moyer >> > Signed-off-by: Pankaj Gupta >> >> There's a slight change in behavior for the error path in the >> virtio_pmem driver. Previously, all errors from virtio_pmem_flush were >> converted to -EIO. Now, they are reported as-is. I think this is >> actually an improvement. >> >> I'll also note that the current behavior can result in data corruption, >> so this should be tagged for stable. > > I added that and was about to push this out, but what about the fact > that now the guest will synchronously wait for flushing to occur. The > goal of the child bio was to allow that to be an I/O wait with > overlapping I/O, or at least not blocking the submission thread. Does > the block layer synchronously wait for PREFLUSH requests? You *have* to wait for the preflush to complete before issuing the data write. See the "Explicit cache flushes" section in Documentation/block/writeback_cache_control.rst. -Jeff