RFR: Fix race condition in jdwp
Andrew Leonard
andrew_m_leonard at uk.ibm.com
Wed Apr 11 08:29:16 UTC 2018
Thanks Serguei,
I terms of a standalone testcase it is quite tricky, as due to the nature
of the issue which took a lot of investigation to solve it's very timing
dependent and will only occur randomly. It can be forced as I indicated
below by adding a "sleep" in the VMInit report code but that's not a
testcase, however the issue was originally found in our JCK testing for
IBMJava8, testcase test.jck8b.runtime.vm.jdwp, but again only happened
intermittently. Sort of like "performance" type issues we're not always
going to be able to create a testcase that will always "fail" if the fix
is not present.
Your thoughts?
Cheers
Andrew
Andrew Leonard
Java Runtimes Development
IBM Hursley
IBM United Kingdom Ltd
Phone internal: 245913, external: 01962 815913
internet email: andrew_m_leonard at uk.ibm.com
From: "serguei.spitsyn at oracle.com" <serguei.spitsyn at oracle.com>
To: Andrew Leonard <andrew_m_leonard at uk.ibm.com>
Cc: serviceability-dev at openjdk.java.net
Date: 11/04/2018 01:02
Subject: Re: RFR: Fix race condition in jdwp
Hi Andrew,
Okay, I'll file a bug on this topic.
But do you have a standalone test demonstrating this issue?
Thanks,
Serguei
On 4/10/18 06:23, Andrew Leonard wrote:
Hi Serguei,
I don't have access to the bug database to raise one, are you able to
please?
Summary: JDWP debugger initialization hangs intermittently
Description: If during the JDWP setup initialization the VM initialization
takes slightly longer than the main debug initialization thread a "hang"
situation can occur. This has been seen in testcase
test.jck8b.runtime.vm.jdwp and can also be recreated easily by adding a 10
second sleep to the beginning of the
src/jdk.jdwp.agent/share/native/libjdwp/eventHelper.c method
eventHelper_reportVMInit() .
First seen: JDK8
Recreated: JDK11
Thanks
Andrew
Andrew Leonard
Java Runtimes Development
IBM Hursley
IBM United Kingdom Ltd
Phone internal: 245913, external: 01962 815913
internet email: andrew_m_leonard at uk.ibm.com
From: "serguei.spitsyn at oracle.com" <serguei.spitsyn at oracle.com>
To: Andrew Leonard <andrew_m_leonard at uk.ibm.com>,
serviceability-dev at openjdk.java.net
Date: 09/04/2018 23:03
Subject: Re: RFR: Fix race condition in jdwp
Hi Andrew,
The patch itself looks reasonable.
However, in order to proceed with it, a bug report with a standalone
test case demonstrating the issue is needed.
Thanks,
Serguei
On 4/9/18 09:07, Andrew Leonard wrote:
> Hi,
> We discovered in our testing with OpenJ9 that a race condition can
> occur in the jdwp under certain circumstances, and we were able to
> force the same issue with Hotspot. Normally, the event helper thread
> suspends all threads, then the debug loop in the listener thread
> receives a command to resume. The debugger may deadlock if the debug
> loop in the listener thread starts processing commands (e.g. resume
> threads) before the event helper completes the initialization (and
> suspends threads).
>
> This patch adds synchronization to ensure the event helper completes
> the initialization sequence before debugger commands are processed.
>
> Please can I find a sponsor for this contribution? Patch below..
>
> Many thanks
>
> Andrew
>
>
>
> diff --git a/src/jdk.jdwp.agent/share/native/libjdwp/debugInit.c
> b/src/jdk.jdwp.agent/share/native/libjdwp/debugInit.c
> --- a/src/jdk.jdwp.agent/share/native/libjdwp/debugInit.c
> +++ b/src/jdk.jdwp.agent/share/native/libjdwp/debugInit.c
> @@ -1,5 +1,5 @@
> /*
> - * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights
> reserved.
> + * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights
> reserved.
> * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
> *
> * This code is free software; you can redistribute it and/or modify it
> @@ -58,6 +58,7 @@
> static jboolean vmInitialized;
> static jrawMonitorID initMonitor;
> static jboolean initComplete;
> +static jboolean VMInitComplete;
> static jbyte currentSessionID;
>
> /*
> @@ -617,6 +618,35 @@
> debugMonitorExit(initMonitor);
> }
>
> +/*
> + * Signal VM initialization is complete.
> + */
> +void
> +signalVMInitComplete(void)
> +{
> + /*
> + * VM Initialization is complete
> + */
> + LOG_MISC(("signal VM initialization complete"));
> + debugMonitorEnter(initMonitor);
> + VMInitComplete = JNI_TRUE;
> + debugMonitorNotifyAll(initMonitor);
> + debugMonitorExit(initMonitor);
> +}
> +
> +/*
> + * Wait for VM initialization to complete.
> + */
> +void
> +debugInit_waitVMInitComplete(void)
> +{
> + debugMonitorEnter(initMonitor);
> + while (!VMInitComplete) {
> + debugMonitorWait(initMonitor);
> + }
> + debugMonitorExit(initMonitor);
> +}
> +
> /* All process exit() calls come from here */
> void
> forceExit(int exit_code)
> @@ -672,6 +702,7 @@
> LOG_MISC(("Begin initialize()"));
> currentSessionID = 0;
> initComplete = JNI_FALSE;
> + VMInitComplete = JNI_FALSE;
>
> if ( gdata->vmDead ) {
> EXIT_ERROR(AGENT_ERROR_INTERNAL,"VM dead at initialize() time");
> diff --git a/src/jdk.jdwp.agent/share/native/libjdwp/debugInit.h
> b/src/jdk.jdwp.agent/share/native/libjdwp/debugInit.h
> --- a/src/jdk.jdwp.agent/share/native/libjdwp/debugInit.h
> +++ b/src/jdk.jdwp.agent/share/native/libjdwp/debugInit.h
> @@ -1,5 +1,5 @@
> /*
> - * Copyright (c) 1998, 2015, Oracle and/or its affiliates. All rights
> reserved.
> + * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights
> reserved.
> * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
> *
> * This code is free software; you can redistribute it and/or modify it
> @@ -39,4 +39,7 @@
> void debugInit_exit(jvmtiError, const char *);
> void forceExit(int);
>
> +void debugInit_waitVMInitComplete(void);
> +void signalVMInitComplete(void);
> +
> #endif
> diff --git a/src/jdk.jdwp.agent/share/native/libjdwp/debugLoop.c
> b/src/jdk.jdwp.agent/share/native/libjdwp/debugLoop.c
> --- a/src/jdk.jdwp.agent/share/native/libjdwp/debugLoop.c
> +++ b/src/jdk.jdwp.agent/share/native/libjdwp/debugLoop.c
> @@ -1,5 +1,5 @@
> /*
> - * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights
> reserved.
> + * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights
> reserved.
> * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
> *
> * This code is free software; you can redistribute it and/or modify it
> @@ -98,6 +98,7 @@
> standardHandlers_onConnect();
> threadControl_onConnect();
>
> + debugInit_waitVMInitComplete();
> /* Okay, start reading cmds! */
> while (shouldListen) {
> if (!dequeue(&p)) {
> diff --git a/src/jdk.jdwp.agent/share/native/libjdwp/eventHelper.c
> b/src/jdk.jdwp.agent/share/native/libjdwp/eventHelper.c
> --- a/src/jdk.jdwp.agent/share/native/libjdwp/eventHelper.c
> +++ b/src/jdk.jdwp.agent/share/native/libjdwp/eventHelper.c
> @@ -1,5 +1,5 @@
> /*
> - * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights
> reserved.
> + * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights
> reserved.
> * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
> *
> * This code is free software; you can redistribute it and/or modify it
> @@ -580,6 +580,7 @@
> (void)threadControl_suspendThread(command->thread, JNI_FALSE);
> }
>
> + signalVMInitComplete();
> outStream_initCommand(&out, uniqueID(), 0x0,
> JDWP_COMMAND_SET(Event),
> JDWP_COMMAND(Event, Composite));
>
>
>
> Andrew Leonard
> Java Runtimes Development
> IBM Hursley
> IBM United Kingdom Ltd
> Phone internal: 245913, external: 01962 815913
> internet email: andrew_m_leonard at uk.ibm.com
>
>
> Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with
> number 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
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