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 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 1107BC433FE for ; Tue, 15 Nov 2022 12:28:31 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ouuob-0004DG-2Q; Tue, 15 Nov 2022 07:13:21 -0500 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 1ouuoU-000460-Co for qemu-devel@nongnu.org; Tue, 15 Nov 2022 07:13:17 -0500 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 1ouuoS-0004cy-Ue for qemu-devel@nongnu.org; Tue, 15 Nov 2022 07:13:14 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668514392; 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=8sTZ2tLPTwfI8PVRQNhye5uLdMdQcsdyAavf636xeAI=; b=E3oFS/X4rohgISzyTZ8AhlWUM0QN4Qj1TilZEFkGIOjYOz/XCd4jSWXoAORFjAU8+TFSLP Wu7Uakz49iRwltsFVKao4ODhuMpFVCnaGOvStY8GOv8eBCjrCPPv+Wt2C0/W1IqJ8ugFhC EgL8rzfCknMSCnOX/GNXR+F34jQsxCw= 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-615-_8tfqTi3PW-qJrKLiwU84A-1; Tue, 15 Nov 2022 07:13:09 -0500 X-MC-Unique: _8tfqTi3PW-qJrKLiwU84A-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 77BEA811E75; Tue, 15 Nov 2022 12:13:08 +0000 (UTC) Received: from secure.mitica (unknown [10.39.195.11]) by smtp.corp.redhat.com (Postfix) with ESMTP id EE63F492B05; Tue, 15 Nov 2022 12:13:05 +0000 (UTC) From: Juan Quintela To: qemu-devel@nongnu.org Cc: Paolo Bonzini , David Hildenbrand , Laurent Vivier , Stefan Hajnoczi , Fam Zheng , qemu-block@nongnu.org, "Dr. David Alan Gilbert" , Thomas Huth , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , qemu-trivial@nongnu.org, Michael Tokarev , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Peter Xu , Juan Quintela Subject: [PATCH 10/30] migration: Fix possible infinite loop of ram save process Date: Tue, 15 Nov 2022 13:12:06 +0100 Message-Id: <20221115121226.26609-11-quintela@redhat.com> In-Reply-To: <20221115121226.26609-1-quintela@redhat.com> References: <20221115121226.26609-1-quintela@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.129.124; 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=unavailable 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 From: Peter Xu When starting ram saving procedure (especially at the completion phase), always set last_seen_block to non-NULL to make sure we can always correctly detect the case where "we've migrated all the dirty pages". Then we'll guarantee both last_seen_block and pss.block will be valid always before the loop starts. See the comment in the code for some details. Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Peter Xu Reviewed-by: Juan Quintela Signed-off-by: Juan Quintela --- migration/ram.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/migration/ram.c b/migration/ram.c index bb4f08bfed..c0f5d6d287 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -2574,14 +2574,22 @@ static int ram_find_and_save_block(RAMState *rs) return pages; } + /* + * Always keep last_seen_block/last_page valid during this procedure, + * because find_dirty_block() relies on these values (e.g., we compare + * last_seen_block with pss.block to see whether we searched all the + * ramblocks) to detect the completion of migration. Having NULL value + * of last_seen_block can conditionally cause below loop to run forever. + */ + if (!rs->last_seen_block) { + rs->last_seen_block = QLIST_FIRST_RCU(&ram_list.blocks); + rs->last_page = 0; + } + pss.block = rs->last_seen_block; pss.page = rs->last_page; pss.complete_round = false; - if (!pss.block) { - pss.block = QLIST_FIRST_RCU(&ram_list.blocks); - } - do { again = true; found = get_queued_page(rs, &pss); -- 2.38.1