From patchwork Wed Sep 6 19:01:39 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 13375898 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 947C7EE14D6 for ; Wed, 6 Sep 2023 19:02:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qdxmm-0006BB-2Q; Wed, 06 Sep 2023 15:01:56 -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 1qdxmh-00069x-Ax for qemu-devel@nongnu.org; Wed, 06 Sep 2023 15:01:51 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qdxme-00087M-JY for qemu-devel@nongnu.org; Wed, 06 Sep 2023 15:01:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1694026907; 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=tUCOewx5Uk4Y3QQOUxCFtRBKpEhPDosHOt7NC6SB8DA=; b=L9rW+8iY6jTXxpUmXzeULf4psPz/+BmkvG2bLd3W/py8y/Zd4NKrCCDmRNbK2RZbNMLEx7 R0OvlUzM9vgY4kWKx7GbUG3lltNT487DJTnJAFfsa5mWUAWjlx8j7ydcOibfGZWQiK9iYQ +ZIfShPMa4FnNiEB0zEo6WKecZH88ho= 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-512-g3qDoFB3O2G6eete1x3mkg-1; Wed, 06 Sep 2023 15:01:46 -0400 X-MC-Unique: g3qDoFB3O2G6eete1x3mkg-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8746D88DF61; Wed, 6 Sep 2023 19:01:45 +0000 (UTC) Received: from localhost (unknown [10.39.193.221]) by smtp.corp.redhat.com (Postfix) with ESMTP id 14B88493110; Wed, 6 Sep 2023 19:01:44 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: "Dr. David Alan Gilbert" , Eduardo Habkost , pbonzini@redhat.com, Markus Armbruster , Eric Blake , kwolf@redhat.com, Maxim Levitsky , =?utf-8?q?Daniel_P?= =?utf-8?q?=2E_Berrang=C3=A9?= , Stefan Hajnoczi Subject: [RFC 1/3] hmp: avoid the nested event loop in handle_hmp_command() Date: Wed, 6 Sep 2023 15:01:39 -0400 Message-ID: <20230906190141.1286893-2-stefanha@redhat.com> In-Reply-To: <20230906190141.1286893-1-stefanha@redhat.com> References: <20230906190141.1286893-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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 Coroutine HMP commands currently run to completion in a nested event loop with the Big QEMU Lock (BQL) held. The call_rcu thread also uses the BQL and cannot process work while the coroutine monitor command is running. A deadlock occurs when monitor commands attempt to wait for call_rcu work to finish. This patch refactors the HMP monitor to use the existing event loop instead of creating a nested event loop. This will allow the next patches to rely on draining call_rcu work. Signed-off-by: Stefan Hajnoczi --- monitor/hmp.c | 28 +++++++++++++++------------- 1 file changed, 15 insertions(+), 13 deletions(-) diff --git a/monitor/hmp.c b/monitor/hmp.c index 69c1b7e98a..6cff2810aa 100644 --- a/monitor/hmp.c +++ b/monitor/hmp.c @@ -1111,15 +1111,17 @@ typedef struct HandleHmpCommandCo { Monitor *mon; const HMPCommand *cmd; QDict *qdict; - bool done; } HandleHmpCommandCo; -static void handle_hmp_command_co(void *opaque) +static void coroutine_fn handle_hmp_command_co(void *opaque) { HandleHmpCommandCo *data = opaque; + handle_hmp_command_exec(data->mon, data->cmd, data->qdict); monitor_set_cur(qemu_coroutine_self(), NULL); - data->done = true; + qobject_unref(data->qdict); + monitor_resume(data->mon); + g_free(data); } void handle_hmp_command(MonitorHMP *mon, const char *cmdline) @@ -1157,20 +1159,20 @@ void handle_hmp_command(MonitorHMP *mon, const char *cmdline) Monitor *old_mon = monitor_set_cur(qemu_coroutine_self(), &mon->common); handle_hmp_command_exec(&mon->common, cmd, qdict); monitor_set_cur(qemu_coroutine_self(), old_mon); + qobject_unref(qdict); } else { - HandleHmpCommandCo data = { - .mon = &mon->common, - .cmd = cmd, - .qdict = qdict, - .done = false, - }; - Coroutine *co = qemu_coroutine_create(handle_hmp_command_co, &data); + HandleHmpCommandCo *data; /* freed by handle_hmp_command_co() */ + + data = g_new(HandleHmpCommandCo, 1); + data->mon = &mon->common; + data->cmd = cmd; + data->qdict = qdict; /* freed by handle_hmp_command_co() */ + + Coroutine *co = qemu_coroutine_create(handle_hmp_command_co, data); + monitor_suspend(&mon->common); /* resumed by handle_hmp_command_co() */ monitor_set_cur(co, &mon->common); aio_co_enter(qemu_get_aio_context(), co); - AIO_WAIT_WHILE_UNLOCKED(NULL, !data.done); } - - qobject_unref(qdict); } static void cmd_completion(MonitorHMP *mon, const char *name, const char *list)