From patchwork Mon Jul 22 13:33:44 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Max Reitz X-Patchwork-Id: 11052385 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 662B3746 for ; Mon, 22 Jul 2019 13:34:46 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 559D3284C9 for ; Mon, 22 Jul 2019 13:34:46 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 4A25D286D6; Mon, 22 Jul 2019 13:34:46 +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=-5.2 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id BE2EA28676 for ; Mon, 22 Jul 2019 13:34:45 +0000 (UTC) Received: from localhost ([::1]:33642 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hpYSi-0000Im-Vm for patchwork-qemu-devel@patchwork.kernel.org; Mon, 22 Jul 2019 09:34:44 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:52835) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hpYSO-0007WY-6k for qemu-devel@nongnu.org; Mon, 22 Jul 2019 09:34:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hpYSM-0005Fg-U1 for qemu-devel@nongnu.org; Mon, 22 Jul 2019 09:34:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53086) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hpYSK-0005BT-9u; Mon, 22 Jul 2019 09:34:20 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9B7AC308212D; Mon, 22 Jul 2019 13:34:19 +0000 (UTC) Received: from localhost (unknown [10.40.205.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C697E60A97; Mon, 22 Jul 2019 13:34:15 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Date: Mon, 22 Jul 2019 15:33:44 +0200 Message-Id: <20190722133347.15122-3-mreitz@redhat.com> In-Reply-To: <20190722133347.15122-1-mreitz@redhat.com> References: <20190722133347.15122-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Mon, 22 Jul 2019 13:34:19 +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: [Qemu-devel] [PATCH v3 2/5] block: Reduce (un)drains when replacing a child 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: Kevin Wolf , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP Currently, bdrv_replace_child_noperm() undrains the parent until it is completely undrained, then re-drains it after attaching the new child node. This is a problem with bdrv_drop_intermediate(): We want to keep the whole subtree drained, including parents, while the operation is under way. bdrv_replace_child_noperm() breaks this by allowing every parent to become unquiesced briefly, and then redraining it. In fact, there is no reason why the parent should become unquiesced and be allowed to submit requests to the new child node if that new node is supposed to be kept drained. So if anything, we have to drain the parent before detaching the old child node. Conversely, we have to undrain it only after attaching the new child node. Thus, change the whole drain algorithm here: Calculate the number of times we have to drain/undrain the parent before replacing the child node then drain it (if necessary), replace the child node, and then undrain it. Signed-off-by: Max Reitz --- block.c | 49 +++++++++++++++++++++++++++++++++---------------- 1 file changed, 33 insertions(+), 16 deletions(-) diff --git a/block.c b/block.c index 818885d467..153e2a8805 100644 --- a/block.c +++ b/block.c @@ -2238,13 +2238,27 @@ static void bdrv_replace_child_noperm(BdrvChild *child, BlockDriverState *new_bs) { BlockDriverState *old_bs = child->bs; - int i; + int new_bs_quiesce_counter; + int drain_saldo; assert(!child->frozen); if (old_bs && new_bs) { assert(bdrv_get_aio_context(old_bs) == bdrv_get_aio_context(new_bs)); } + + new_bs_quiesce_counter = (new_bs ? new_bs->quiesce_counter : 0); + drain_saldo = new_bs_quiesce_counter - child->parent_quiesce_counter; + + /* + * If the new child node is drained but the old one was not, flush + * all outstanding requests to the old child node. + */ + while (drain_saldo > 0 && child->role->drained_begin) { + bdrv_parent_drained_begin_single(child, true); + drain_saldo--; + } + if (old_bs) { /* Detach first so that the recursive drain sections coming from @child * are already gone and we only end the drain sections that came from @@ -2252,28 +2266,22 @@ static void bdrv_replace_child_noperm(BdrvChild *child, if (child->role->detach) { child->role->detach(child); } - while (child->parent_quiesce_counter) { - bdrv_parent_drained_end_single(child); - } QLIST_REMOVE(child, next_parent); - } else { - assert(child->parent_quiesce_counter == 0); } child->bs = new_bs; if (new_bs) { QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent); - if (new_bs->quiesce_counter) { - int num = new_bs->quiesce_counter; - if (child->role->parent_is_bds) { - num -= bdrv_drain_all_count; - } - assert(num >= 0); - for (i = 0; i < num; i++) { - bdrv_parent_drained_begin_single(child, true); - } - } + + /* + * Detaching the old node may have led to the new node's + * quiesce_counter having been decreased. Not a problem, we + * just need to recognize this here and then invoke + * drained_end appropriately more often. + */ + assert(new_bs->quiesce_counter <= new_bs_quiesce_counter); + drain_saldo += new_bs->quiesce_counter - new_bs_quiesce_counter; /* Attach only after starting new drained sections, so that recursive * drain sections coming from @child don't get an extra .drained_begin @@ -2282,6 +2290,15 @@ static void bdrv_replace_child_noperm(BdrvChild *child, child->role->attach(child); } } + + /* + * If the old child node was drained but the new one is not, allow + * requests to come in only after the new node has been attached. + */ + while (drain_saldo < 0 && child->role->drained_end) { + bdrv_parent_drained_end_single(child); + drain_saldo++; + } } /*