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 48E6FC433FE for ; Mon, 21 Nov 2022 13:00:10 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ox6OU-0001a0-J1; Mon, 21 Nov 2022 07:59:26 -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 1ox6OT-0001Za-AN for qemu-devel@nongnu.org; Mon, 21 Nov 2022 07:59:25 -0500 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 1ox6OR-0006Qj-TY for qemu-devel@nongnu.org; Mon, 21 Nov 2022 07:59:25 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669035563; 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=C43sXzuDPrCVxw3vYvZA3vkx4qjmhBG5GAMoIDyKDro=; b=YOJzGVdwAtnOnGSRfnOZiNZGFRu27wFDlPCh5oaf4VWxigpAb8x1653mhpj6MPTASGs8fc E0Yuih6P66O9ZCFUZLuSKOeMqGcJ3JIlg0SNyZPVjszZqY0ppl0T+3ztPT3WzzmtU9ghrq 1/XEAOwt732wVE4a4x56AIGbjf9nmqk= 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-94-clqyI-BYPgiqhT9ZfcFXAA-1; Mon, 21 Nov 2022 07:59:20 -0500 X-MC-Unique: clqyI-BYPgiqhT9ZfcFXAA-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 B3E1C101A528; Mon, 21 Nov 2022 12:59:19 +0000 (UTC) Received: from secure.mitica (unknown [10.39.193.227]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0E12AC15BB3; Mon, 21 Nov 2022 12:59:17 +0000 (UTC) From: Juan Quintela To: qemu-devel@nongnu.org Cc: Stefan Hajnoczi , "Dr. David Alan Gilbert" , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Fam Zheng , Juan Quintela , qemu-block@nongnu.org, David Hildenbrand , Peter Xu , Paolo Bonzini Subject: [PULL 3/8] migration: Fix possible infinite loop of ram save process Date: Mon, 21 Nov 2022 13:59:02 +0100 Message-Id: <20221121125907.62469-4-quintela@redhat.com> In-Reply-To: <20221121125907.62469-1-quintela@redhat.com> References: <20221121125907.62469-1-quintela@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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+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 dc1de9ddbc..1d42414ecc 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -2546,14 +2546,22 @@ 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