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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 18FA9C48BD5 for ; Tue, 25 Jun 2019 08:15:47 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E5AFA214DA for ; Tue, 25 Jun 2019 08:15:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E5AFA214DA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:57404 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hfgcC-0002jD-VX for qemu-devel@archiver.kernel.org; Tue, 25 Jun 2019 04:15:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48431) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hfgaL-0001VQ-SX for qemu-devel@nongnu.org; Tue, 25 Jun 2019 04:13:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hfgaK-0000YN-UL for qemu-devel@nongnu.org; Tue, 25 Jun 2019 04:13:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33808) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hfgaA-0000Ju-1H; Tue, 25 Jun 2019 04:13:39 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 37803308626C; Tue, 25 Jun 2019 08:13:35 +0000 (UTC) Received: from localhost.localdomain (ovpn-117-23.ams2.redhat.com [10.36.117.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6495A1001B00; Tue, 25 Jun 2019 08:13:33 +0000 (UTC) Date: Tue, 25 Jun 2019 10:13:31 +0200 From: Kevin Wolf To: Andrey Shinkevich Message-ID: <20190625081331.GB5187@localhost.localdomain> References: <1560276131-683243-1-git-send-email-andrey.shinkevich@virtuozzo.com> <1560276131-683243-8-git-send-email-andrey.shinkevich@virtuozzo.com> <20190617114544.GE7397@linux.fritz.box> <09632364-3d1d-9e5c-a050-f48f76d2e38c@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <09632364-3d1d-9e5c-a050-f48f76d2e38c@virtuozzo.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Tue, 25 Jun 2019 08:13:35 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 7/7] iotests: new file to suppress Valgrind errors X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Vladimir Sementsov-Ogievskiy , "berrange@redhat.com" , Denis Lunev , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" , "mreitz@redhat.com" , Roman Kagan Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 24.06.2019 um 18:55 hat Andrey Shinkevich geschrieben: > > > On 17/06/2019 14:45, Kevin Wolf wrote: > > Am 11.06.2019 um 20:02 hat Andrey Shinkevich geschrieben: > >> The Valgrind tool reports about an uninitialised memory usage when the > >> initialization is actually not needed. For example, the buffer 'buf' > >> instantiated on a stack of the function guess_disk_lchs(). > > > > I would be careful with calling initialisation "not needed". It means > > that the test case may not behave entirely determinstic because the > > uninitialised memory can vary between runs.\ > > I am going to amend the comment. > > Andrey > > > > > In this specific case, I assume that guess_disk_lchs() is called for a > > null block node, for which .bdrv_co_preadv by default returns without > > actually writing to the buffer. Instead of ignoring the valgrind error, > > we could instead pass read-zeroes=on to the null block driver to make > > the test deterministic. > > The buffer that the Valgrind complains of is initialized by the > following function call blk_pread_unthrottled() that reads the first > BDRV_SECTOR_SIZE bytes form a disk "to guess the disk logical geometry". > The Valgrind does not recognize that way of initialization. I believe we > do not need to zero the buffer instantiated on the stack just to make > the Valgrind silent there. My point is that blk_pread_unthrottled() with null-co/null-aio leaves the buffer untouched if read-zeroes=off (which is the default). So yes, valgrind is right, this memory is still uninitialised after blk_pread_unthrottled(). Kevin