SIGBUS on linux in perfMemory_init

[Ioi Lam]

On 5/5/2022 11:06 AM, Ioi Lam wrote:
>
>
> On 5/5/2022 3:05 AM, Severin Gehwolf wrote:
>> On Wed, 2022-05-04 at 12:13 -0700, Ioi Lam wrote:
>>> ====================================
>>>
>>> How about this:
>>>
>>> When a JVM starts up, it creates the hsperfdata with a UUID instead of
>>> PID. E.g.,
>>>
>>>       /tmp/hsperfdata_user/0da29ace76f76f61
>>>
>>> Today, jps reads /proc/*/status to determine the NSpid, so we are doing
>>> a lot of processing already. Instead, we should read /proc/*/maps and
>>> scan for something with this pattern:
>>>
>>>       7ffb2536d000-7ffb25375000 rw-s ....
>>> /tmp/hsperfdata_user/0da29ace76f76f61
>>>
>>> If we can find this pattern, we know we have a JVM process that the
>>> current user can attach to.
>>>
>>> When attaching to this process, we will use this file instead
>>>
>>> /proc/$PID/root/tmp/.java_pid0da29ace76f76f61
>>>
>>> This should work with
>>>
>>> - shared /tmp across containers
>>> - nested containers
>> Wouldn't this break with the work-around Vitaly employed? I.e. using
>>
>> -XX:+PerfDisableSharedMem
>>
>> $ ps ax | grep java
>>    10449 pts/4    Sl+    0:00 
>> ./build/linux-x86_64-normal-server-fastdebug/images/jdk/bin/java 
>> -XX:+PerfDisableSharedMem Hello
>>    10744 pts/5    S+     0:00 grep --color=auto java
>> $ grep hsperf /proc/10449/maps
>> $ jcmd 10449 VM.version
>> 10449:
>> OpenJDK 64-Bit Server VM version 
>> 11.0.16-internal+0-adhoc.sgehwolf.jdk11u-dev
>> JDK 11.0.16
>> $ jcmd -l
>> 10857 jdk.jcmd/sun.tools.jcmd.JCmd -l
>
> I think we can create a fake mmap region when 
> -XX:+PerfDisableSharedMem is used. E.g.,
>
> 7ffb2536d000-7ffb25375000 rw-s .... 
> /tmp/hsperfdata_user/0da29ace76f76f61-disabled
>
> So we can reliably discover the .java_pidxxxxx file used for attachment:
>
> jcmd $PID
> -> /proc/$PID/maps
> -> /tmp/hsperfdata_user/0da29ace76f76f61-disabled
> -> /proc/$PID/root/tmp/.java_pid0da29ace76f76f61
>

An alternative is to set an environment variable like 
JVM_ATTACH_UUID=0da29ace76f76f61 and we can get that from 
/proc/*/environ , which might be more light-weight.


> Thanks
> - Ioi
>
>
>>
>> Basically, by departing from using system identifiers, we need some
>> other way to discover the well known identifier.
>>
>> Thanks,
>> Severin
>>
>>
>