From patchwork Thu May 4 19:53:08 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 13231737 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 08668C77B78 for ; Thu, 4 May 2023 19:59:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1puf1N-0005mJ-Il; Thu, 04 May 2023 15:53:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1puf1L-0005kh-Bm for qemu-devel@nongnu.org; Thu, 04 May 2023 15:53:43 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1puf1J-0006PY-Ma for qemu-devel@nongnu.org; Thu, 04 May 2023 15:53:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683230021; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2q86JTUb82jHsKou8iDv6+YsV2u1chyoHCqSrVQuj0g=; b=B5pQAGBnnAr0A+0xGh0wbuAruZ1+g+47gWo6+eRRnLbwl9zPOfvj1q63v6OuTe5vKic0M2 bvAcYiZhsT4glR8IbJYeqRoykfg+/DtaLLX8Zxd+7p20mKLEZMUvxn7GJjzKIwAVZC4QKu yLIcmabUUUiXUP7+hkyj2v2WoEDXtQ0= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-403-PWDrmmbSNeKjFAv3qLOnZg-1; Thu, 04 May 2023 15:53:37 -0400 X-MC-Unique: PWDrmmbSNeKjFAv3qLOnZg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 31E0D109DCE5; Thu, 4 May 2023 19:53:36 +0000 (UTC) Received: from localhost (unknown [10.39.192.57]) by smtp.corp.redhat.com (Postfix) with ESMTP id 59BEFC15BAD; Thu, 4 May 2023 19:53:35 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Ronnie Sahlberg , Aarushi Mehta , qemu-block@nongnu.org, Paul Durrant , Anthony Perard , Peter Lieven , Stefan Weil , Xie Yongji , Kevin Wolf , Paolo Bonzini , "Michael S. Tsirkin" , Leonardo Bras , Peter Xu , Hanna Reitz , Stefano Stabellini , Richard Henderson , David Woodhouse , Coiby Xu , Eduardo Habkost , Stefano Garzarella , =?utf-8?q?Philippe_Mathieu-Daud?= =?utf-8?q?=C3=A9?= , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= , Stefan Hajnoczi , Julia Suvorova , xen-devel@lists.xenproject.org, eesposit@redhat.com, Juan Quintela , "Richard W.M. Jones" , Fam Zheng , Marcel Apfelbaum Subject: [PATCH v5 02/21] block-backend: split blk_do_set_aio_context() Date: Thu, 4 May 2023 15:53:08 -0400 Message-Id: <20230504195327.695107-3-stefanha@redhat.com> In-Reply-To: <20230504195327.695107-1-stefanha@redhat.com> References: <20230504195327.695107-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.161, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org blk_set_aio_context() is not fully transactional because blk_do_set_aio_context() updates blk->ctx outside the transaction. Most of the time this goes unnoticed but a BlockDevOps.drained_end() callback that invokes blk_get_aio_context() fails assert(ctx == blk->ctx). This happens because blk->ctx is only assigned after BlockDevOps.drained_end() is called and we're in an intermediate state where BlockDrvierState nodes already have the new context and the BlockBackend still has the old context. Making blk_set_aio_context() fully transactional solves this assertion failure because the BlockBackend's context is updated as part of the transaction (before BlockDevOps.drained_end() is called). Split blk_do_set_aio_context() in order to solve this assertion failure. This helper function actually serves two different purposes: 1. It drives blk_set_aio_context(). 2. It responds to BdrvChildClass->change_aio_ctx(). Get rid of the helper function. Do #1 inside blk_set_aio_context() and do #2 inside blk_root_set_aio_ctx_commit(). This simplifies the code. The only drawback of the fully transactional approach is that blk_set_aio_context() must contend with blk_root_set_aio_ctx_commit() being invoked as part of the AioContext change propagation. This can be solved by temporarily setting blk->allow_aio_context_change to true. Future patches call blk_get_aio_context() from BlockDevOps->drained_end(), so this patch will become necessary. Signed-off-by: Stefan Hajnoczi --- block/block-backend.c | 71 +++++++++++++++++-------------------------- 1 file changed, 28 insertions(+), 43 deletions(-) diff --git a/block/block-backend.c b/block/block-backend.c index fc530ded6a..68d38635bc 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -2205,52 +2205,31 @@ static AioContext *blk_aiocb_get_aio_context(BlockAIOCB *acb) return blk_get_aio_context(blk_acb->blk); } -static int blk_do_set_aio_context(BlockBackend *blk, AioContext *new_context, - bool update_root_node, Error **errp) -{ - BlockDriverState *bs = blk_bs(blk); - ThrottleGroupMember *tgm = &blk->public.throttle_group_member; - int ret; - - if (bs) { - bdrv_ref(bs); - - if (update_root_node) { - /* - * update_root_node MUST be false for blk_root_set_aio_ctx_commit(), - * as we are already in the commit function of a transaction. - */ - ret = bdrv_try_change_aio_context(bs, new_context, blk->root, errp); - if (ret < 0) { - bdrv_unref(bs); - return ret; - } - } - /* - * Make blk->ctx consistent with the root node before we invoke any - * other operations like drain that might inquire blk->ctx - */ - blk->ctx = new_context; - if (tgm->throttle_state) { - bdrv_drained_begin(bs); - throttle_group_detach_aio_context(tgm); - throttle_group_attach_aio_context(tgm, new_context); - bdrv_drained_end(bs); - } - - bdrv_unref(bs); - } else { - blk->ctx = new_context; - } - - return 0; -} - int blk_set_aio_context(BlockBackend *blk, AioContext *new_context, Error **errp) { + bool old_allow_change; + BlockDriverState *bs = blk_bs(blk); + int ret; + GLOBAL_STATE_CODE(); - return blk_do_set_aio_context(blk, new_context, true, errp); + + if (!bs) { + blk->ctx = new_context; + return 0; + } + + bdrv_ref(bs); + + old_allow_change = blk->allow_aio_context_change; + blk->allow_aio_context_change = true; + + ret = bdrv_try_change_aio_context(bs, new_context, NULL, errp); + + blk->allow_aio_context_change = old_allow_change; + + bdrv_unref(bs); + return ret; } typedef struct BdrvStateBlkRootContext { @@ -2262,8 +2241,14 @@ static void blk_root_set_aio_ctx_commit(void *opaque) { BdrvStateBlkRootContext *s = opaque; BlockBackend *blk = s->blk; + AioContext *new_context = s->new_ctx; + ThrottleGroupMember *tgm = &blk->public.throttle_group_member; - blk_do_set_aio_context(blk, s->new_ctx, false, &error_abort); + blk->ctx = new_context; + if (tgm->throttle_state) { + throttle_group_detach_aio_context(tgm); + throttle_group_attach_aio_context(tgm, new_context); + } } static TransactionActionDrv set_blk_root_context = {