From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:39351) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hDjlS-0002N8-2o for qemu-devel@nongnu.org; Tue, 09 Apr 2019 01:57:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hDjlR-0003hm-4O for qemu-devel@nongnu.org; Tue, 09 Apr 2019 01:57:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32768) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hDjlQ-0003hV-S8 for qemu-devel@nongnu.org; Tue, 09 Apr 2019 01:57:45 -0400 From: Markus Armbruster References: <20190407092314.11066-1-thuth@redhat.com> <20190408134517.GA9047@richard> <14147807-8723-adac-dffb-31b7bbd0fc3b@redhat.com> <20190408222601.GR7238@habkost.net> Date: Tue, 09 Apr 2019 07:57:39 +0200 In-Reply-To: <20190408222601.GR7238@habkost.net> (Eduardo Habkost's message of "Mon, 8 Apr 2019 19:26:01 -0300") Message-ID: <87imvniuuk.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH for-4.0] hw/i386/pc: Fix crash when hot-plugging nvdimm on older machine types List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: Thomas Huth , qemu-devel@nongnu.org, Paolo Bonzini , "Michael S. Tsirkin" , Wei Yang , Xiao Guangrong Eduardo Habkost writes: > On Mon, Apr 08, 2019 at 05:06:49PM +0200, Thomas Huth wrote: >> On 08/04/2019 15.45, Wei Yang wrote: > [...] >> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c >> > index 6077d27361..b11f3b15c1 100644 >> > --- a/hw/i386/pc.c >> > +++ b/hw/i386/pc.c >> > @@ -2091,6 +2091,9 @@ static void pc_memory_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev, >> > } >> > >> > hotplug_handler_pre_plug(pcms->acpi_dev, dev, errp); >> > + if (*errp) { >> > + return; >> > + } >> >> Not sure, but I think you can not rely on the fact that the caller set >> *errp = NULL already... that's why it is more common to use a local_err >> variable and error_propagate() for such cases (which is what I did in my >> patch). > > *errp can't be non-NULL (otherwise functions calling error_setg() > would crash). errp can be NULL, though, and that's why you need > a local_err variable. Correct. The big comment in error.h advises: * Receive an error and pass it on to the caller: * Error *err = NULL; * foo(arg, &err); * if (err) { * handle the error... * error_propagate(errp, err); * } * where Error **errp is a parameter, by convention the last one. * * Do *not* "optimize" this to * foo(arg, errp); * if (*errp) { // WRONG! * handle the error... * } * because errp may be NULL! * * But when all you do with the error is pass it on, please use * foo(arg, errp); * for readability. > I'd love to eliminate NULL errp from our codebase, but I couldn't > find a way to do it that is safe and simple (i.e. not letting us > pass NULL errp by mistake and not requiring a macro wrapping > every `&local_err` expression). Also, I'd prefer not not deviate even more from GError. Apropos NULL, we often pass NULL where we really ought to pass &error_abort. 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=-3.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS 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 98CC7C10F0E for ; Tue, 9 Apr 2019 05:58:34 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5A1D920883 for ; Tue, 9 Apr 2019 05:58:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5A1D920883 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 ([127.0.0.1]:35741 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hDjmD-0002jK-Lc for qemu-devel@archiver.kernel.org; Tue, 09 Apr 2019 01:58:33 -0400 Received: from eggs.gnu.org ([209.51.188.92]:39351) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hDjlS-0002N8-2o for qemu-devel@nongnu.org; Tue, 09 Apr 2019 01:57:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hDjlR-0003hm-4O for qemu-devel@nongnu.org; Tue, 09 Apr 2019 01:57:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32768) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hDjlQ-0003hV-S8 for qemu-devel@nongnu.org; Tue, 09 Apr 2019 01:57:45 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id CB1E430833B5; Tue, 9 Apr 2019 05:57:43 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-116-116.ams2.redhat.com [10.36.116.116]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 45A1F5D9C9; Tue, 9 Apr 2019 05:57:41 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id BFCD71138648; Tue, 9 Apr 2019 07:57:39 +0200 (CEST) From: Markus Armbruster To: Eduardo Habkost References: <20190407092314.11066-1-thuth@redhat.com> <20190408134517.GA9047@richard> <14147807-8723-adac-dffb-31b7bbd0fc3b@redhat.com> <20190408222601.GR7238@habkost.net> Date: Tue, 09 Apr 2019 07:57:39 +0200 In-Reply-To: <20190408222601.GR7238@habkost.net> (Eduardo Habkost's message of "Mon, 8 Apr 2019 19:26:01 -0300") Message-ID: <87imvniuuk.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Tue, 09 Apr 2019 05:57:44 +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 for-4.0] hw/i386/pc: Fix crash when hot-plugging nvdimm on older machine types X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Thomas Huth , Xiao Guangrong , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Wei Yang , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Message-ID: <20190409055739.PMhD0UiPYUo9T1FqHREM24XaJYbTiE8qLG2m1fwAgk0@z> Eduardo Habkost writes: > On Mon, Apr 08, 2019 at 05:06:49PM +0200, Thomas Huth wrote: >> On 08/04/2019 15.45, Wei Yang wrote: > [...] >> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c >> > index 6077d27361..b11f3b15c1 100644 >> > --- a/hw/i386/pc.c >> > +++ b/hw/i386/pc.c >> > @@ -2091,6 +2091,9 @@ static void pc_memory_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev, >> > } >> > >> > hotplug_handler_pre_plug(pcms->acpi_dev, dev, errp); >> > + if (*errp) { >> > + return; >> > + } >> >> Not sure, but I think you can not rely on the fact that the caller set >> *errp = NULL already... that's why it is more common to use a local_err >> variable and error_propagate() for such cases (which is what I did in my >> patch). > > *errp can't be non-NULL (otherwise functions calling error_setg() > would crash). errp can be NULL, though, and that's why you need > a local_err variable. Correct. The big comment in error.h advises: * Receive an error and pass it on to the caller: * Error *err = NULL; * foo(arg, &err); * if (err) { * handle the error... * error_propagate(errp, err); * } * where Error **errp is a parameter, by convention the last one. * * Do *not* "optimize" this to * foo(arg, errp); * if (*errp) { // WRONG! * handle the error... * } * because errp may be NULL! * * But when all you do with the error is pass it on, please use * foo(arg, errp); * for readability. > I'd love to eliminate NULL errp from our codebase, but I couldn't > find a way to do it that is safe and simple (i.e. not letting us > pass NULL errp by mistake and not requiring a macro wrapping > every `&local_err` expression). Also, I'd prefer not not deviate even more from GError. Apropos NULL, we often pass NULL where we really ought to pass &error_abort.