RFR(S): 8247533: SA stack walking sometimes fails with sun.jvm.hotspot.debugger.DebuggerException: get_thread_regs failed for a lwp

[Chris Plummer]

On 6/17/20 7:43 PM, David Holmes wrote:
> Hi Chris,
>
> On 18/06/2020 6:34 am, Chris Plummer wrote:
>> Hello,
>>
>> Please help review the following:
>>
>> https://bugs.openjdk.java.net/browse/JDK-8247533
>> http://cr.openjdk.java.net/~cjplummer/8247533/webrev.00/index.html
>>
>> The CR contains all the needed details. Here's a summary of changes 
>> in each file:
>
> The problem sounds to me like a variation of the more general problem 
> of not ensuring a thread is kept alive whilst acting upon it. I don't 
> know how the SA finds these references to the threads it is going to 
> stackwalk, but is it possible to fix this via appropriate uses of 
> ThreadsListHandle/Iterator?
It fetches ThreadsSMRSupport::_java_thread_list.

Keep in mind that once SA attaches, nothing in the VM changes. For 
example, SA can't create a wrapper to a JavaThread, only to have the 
JavaThread be freed later on. It's just not possible.

Chris
>
> Cheers,
> David
>
>> src/jdk.hotspot.agent/linux/native/libsaproc/LinuxDebuggerLocal.cpp
>> src/jdk.hotspot.agent/macosx/native/libsaproc/MacosxDebuggerLocal.m
>> src/jdk.hotspot.agent/windows/native/libsaproc/sawindbg.cpp
>> -Instead of throwing an exception when the OS ThreadID is invalid, 
>> print a warning.
>>
>> src/jdk.hotspot.agent/linux/native/libsaproc/ps_proc.c
>> -Improve a print_debug message
>>
>> src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/debugger/bsd/BsdThread.java 
>>
>> src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/debugger/linux/LinuxThread.java 
>>
>> src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/debugger/windbg/amd64/WindbgAMD64Thread.java 
>>
>> -Deal with the array of registers read in being null due to the OS 
>> ThreadID not being valid.
>>
>> src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/debugger/bsd/BsdDebuggerLocal.java 
>>
>> src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/debugger/linux/LinuxDebuggerLocal.java 
>>
>> -Fix issue with "sun.jvm.hotspot.debugger.DebuggerException" 
>> appearing twice when printing the exception.
>>
>> thanks,
>>
>> Chris