From patchwork Thu Mar 16 15:12:19 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Juan Quintela X-Patchwork-Id: 1757919 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@legolas.ozlabs.org Authentication-Results: legolas.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: legolas.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=UMD1KzAx; dkim-atps=neutral Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by legolas.ozlabs.org (Postfix) with ESMTPS id 4PcrP75mWjz247M for ; Fri, 17 Mar 2023 02:13:15 +1100 (AEDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pcpHb-0001Xo-So; Thu, 16 Mar 2023 11:12:48 -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 1pcpHO-0001QX-U7 for qemu-devel@nongnu.org; Thu, 16 Mar 2023 11:12:35 -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 1pcpHL-0003Hf-Ra for qemu-devel@nongnu.org; Thu, 16 Mar 2023 11:12:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678979550; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Q+QgOHpzztQRoC5XV2gLvUVlYs/raQm+F133uw/FKVs=; b=UMD1KzAx6vfCicMkkjssTqmtPlJiefGZM7UXBr613NorW2DJ/5gnbY/owga0vGNXsb2DMT daDwQ5iDSDUZGaWlJ514abuHdh5lmuZTtjKVR//+w6ewa7w1TcDT9/xKeayhfQl6sl1mwm lEeXmSfj8kIVQYDzXf0a3TXX/M6h1XM= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-60-0ZV6UHcaM3utLVAN_Y76dw-1; Thu, 16 Mar 2023 11:12:28 -0400 X-MC-Unique: 0ZV6UHcaM3utLVAN_Y76dw-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 8A63E2807D76; Thu, 16 Mar 2023 15:12:28 +0000 (UTC) Received: from secure.mitica (unknown [10.39.195.45]) by smtp.corp.redhat.com (Postfix) with ESMTP id 86045492B00; Thu, 16 Mar 2023 15:12:27 +0000 (UTC) From: Juan Quintela To: qemu-devel@nongnu.org Cc: Juan Quintela , "Dr. David Alan Gilbert" , Peter Xu , Peter Maydell , =?utf-8?q?Daniel_P_=2E_Berrang?= =?utf-8?q?=C3=A9?= Subject: [PULL 1/7] migration: Wait on preempt channel in preempt thread Date: Thu, 16 Mar 2023 16:12:19 +0100 Message-Id: <20230316151225.11362-2-quintela@redhat.com> In-Reply-To: <20230316151225.11362-1-quintela@redhat.com> References: <20230316151225.11362-1-quintela@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=quintela@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_H2=-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+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org From: Peter Xu QEMU main thread will wait until dest preempt channel established during processing the LISTEN command (within the whole postcopy PACKAGED data), by waiting on the semaphore postcopy_qemufile_dst_done. That's racy, because it's possible that the dest QEMU main thread hasn't yet accept()ed the new connection when processing the LISTEN event. The sem_wait() will yield the main thread without being able to run anything else including the accept() of the new socket, which can cause deadlock within the main thread. To avoid the race, move the "wait channel" from main thread to the preempt thread right at the start. Reported-by: Peter Maydell Fixes: 5655aab079 ("migration: Postpone postcopy preempt channel to be after main") Reviewed-by: Daniel P. Berrangé Reviewed-by: Juan Quintela Signed-off-by: Peter Xu Signed-off-by: Juan Quintela --- migration/postcopy-ram.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c index f54f44d899..41c0713650 100644 --- a/migration/postcopy-ram.c +++ b/migration/postcopy-ram.c @@ -1197,11 +1197,6 @@ int postcopy_ram_incoming_setup(MigrationIncomingState *mis) } if (migrate_postcopy_preempt()) { - /* - * The preempt channel is established in asynchronous way. Wait - * for its completion. - */ - qemu_sem_wait(&mis->postcopy_qemufile_dst_done); /* * This thread needs to be created after the temp pages because * it'll fetch RAM_CHANNEL_POSTCOPY PostcopyTmpPage immediately. @@ -1668,6 +1663,12 @@ void *postcopy_preempt_thread(void *opaque) qemu_sem_post(&mis->thread_sync_sem); + /* + * The preempt channel is established in asynchronous way. Wait + * for its completion. + */ + qemu_sem_wait(&mis->postcopy_qemufile_dst_done); + /* Sending RAM_SAVE_FLAG_EOS to terminate this thread */ qemu_mutex_lock(&mis->postcopy_prio_thread_mutex); while (1) {