From dev-return-76371-archive-asf-public=cust-asf.ponee.io@zookeeper.apache.org Tue Nov 27 17:46:06 2018 Return-Path: X-Original-To: archive-asf-public@cust-asf.ponee.io Delivered-To: archive-asf-public@cust-asf.ponee.io Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by mx-eu-01.ponee.io (Postfix) with SMTP id F27DF18077A for ; Tue, 27 Nov 2018 17:46:05 +0100 (CET) Received: (qmail 45002 invoked by uid 500); 27 Nov 2018 16:46:05 -0000 Mailing-List: contact dev-help@zookeeper.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: dev@zookeeper.apache.org Delivered-To: mailing list dev@zookeeper.apache.org Received: (qmail 44767 invoked by uid 99); 27 Nov 2018 16:46:05 -0000 Received: from pnap-us-west-generic-nat.apache.org (HELO spamd4-us-west.apache.org) (209.188.14.142) by apache.org (qpsmtpd/0.29) with ESMTP; Tue, 27 Nov 2018 16:46:05 +0000 Received: from localhost (localhost [127.0.0.1]) by spamd4-us-west.apache.org (ASF Mail Server at spamd4-us-west.apache.org) with ESMTP id ED05FC2271 for ; Tue, 27 Nov 2018 16:46:03 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at spamd4-us-west.apache.org X-Spam-Flag: NO X-Spam-Score: -109.501 X-Spam-Level: X-Spam-Status: No, score=-109.501 tagged_above=-999 required=6.31 tests=[ENV_AND_HDR_SPF_MATCH=-0.5, KAM_ASCII_DIVIDERS=0.8, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001, USER_IN_DEF_SPF_WL=-7.5, USER_IN_WHITELIST=-100] autolearn=disabled Received: from mx1-lw-eu.apache.org ([10.40.0.8]) by localhost (spamd4-us-west.apache.org [10.40.0.11]) (amavisd-new, port 10024) with ESMTP id IjIIODqLC_-7 for ; Tue, 27 Nov 2018 16:46:02 +0000 (UTC) Received: from mailrelay1-us-west.apache.org (mailrelay1-us-west.apache.org [209.188.14.139]) by mx1-lw-eu.apache.org (ASF Mail Server at mx1-lw-eu.apache.org) with ESMTP id B74B55F5C6 for ; Tue, 27 Nov 2018 16:46:01 +0000 (UTC) Received: from jira-lw-us.apache.org (unknown [207.244.88.139]) by mailrelay1-us-west.apache.org (ASF Mail Server at mailrelay1-us-west.apache.org) with ESMTP id E9308E02ED for ; Tue, 27 Nov 2018 16:46:00 +0000 (UTC) Received: from jira-lw-us.apache.org (localhost [127.0.0.1]) by jira-lw-us.apache.org (ASF Mail Server at jira-lw-us.apache.org) with ESMTP id B00BB21095 for ; Tue, 27 Nov 2018 16:46:00 +0000 (UTC) Date: Tue, 27 Nov 2018 16:46:00 +0000 (UTC) From: "Michael K. Edwards (JIRA)" To: dev@zookeeper.apache.org Message-ID: In-Reply-To: References: Subject: [jira] [Commented] (ZOOKEEPER-2778) Potential server deadlock between follower sync with leader and follower receiving external connection requests. MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-JIRA-FingerPrint: 30527f35849b9dde25b450d4833f0394 [ https://issues.apache.org/jira/browse/ZOOKEEPER-2778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16700689#comment-16700689 ] Michael K. Edwards commented on ZOOKEEPER-2778: ----------------------------------------------- The current versions of this patch (#719 for master, #707 for branch-3.5) build green and don't have extraneous content. > Potential server deadlock between follower sync with leader and follower receiving external connection requests. > ---------------------------------------------------------------------------------------------------------------- > > Key: ZOOKEEPER-2778 > URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2778 > Project: ZooKeeper > Issue Type: Bug > Components: quorum > Affects Versions: 3.5.3 > Reporter: Michael Han > Assignee: Michael K. Edwards > Priority: Blocker > Labels: pull-request-available > Fix For: 3.6.0, 3.5.5 > > Time Spent: 6h 50m > Remaining Estimate: 0h > > It's possible to have a deadlock during recovery phase. > Found this issue by analyzing thread dumps of "flaky" ReconfigRecoveryTest [1]. . Here is a sample thread dump that illustrates the state of the execution: > {noformat} > [junit] java.lang.Thread.State: BLOCKED > [junit] at org.apache.zookeeper.server.quorum.QuorumPeer.getElectionAddress(QuorumPeer.java:686) > [junit] at org.apache.zookeeper.server.quorum.QuorumCnxManager.initiateConnection(QuorumCnxManager.java:265) > [junit] at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:445) > [junit] at org.apache.zookeeper.server.quorum.QuorumCnxManager.receiveConnection(QuorumCnxManager.java:369) > [junit] at org.apache.zookeeper.server.quorum.QuorumCnxManager$Listener.run(QuorumCnxManager.java:642) > [junit] > [junit] java.lang.Thread.State: BLOCKED > [junit] at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:472) > [junit] at org.apache.zookeeper.server.quorum.QuorumPeer.connectNewPeers(QuorumPeer.java:1438) > [junit] at org.apache.zookeeper.server.quorum.QuorumPeer.setLastSeenQuorumVerifier(QuorumPeer.java:1471) > [junit] at org.apache.zookeeper.server.quorum.Learner.syncWithLeader(Learner.java:520) > [junit] at org.apache.zookeeper.server.quorum.Follower.followLeader(Follower.java:88) > [junit] at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:1133) > {noformat} > The dead lock happens between the quorum peer thread which running the follower that doing sync with leader work, and the listener of the qcm of the same quorum peer that doing the receiving connection work. Basically to finish sync with leader, the follower needs to synchronize on both QV_LOCK and the qmc object it owns; while in the receiver thread to finish setup an incoming connection the thread needs to synchronize on both the qcm object the quorum peer owns, and the same QV_LOCK. It's easy to see the problem here is the order of acquiring two locks are different, thus depends on timing / actual execution order, two threads might end up acquiring one lock while holding another. > [1] org.apache.zookeeper.server.quorum.ReconfigRecoveryTest.testCurrentServersAreObserversInNextConfig -- This message was sent by Atlassian JIRA (v7.6.3#76005)