RFR(10)(M): 8179498: attach in linux should be relative to /proc/pid/root and namespace aware

[Chris Plummer]

On 9/13/17 9:00 PM, David Holmes wrote:
> Hi Chris,
>
> On 14/09/2017 1:03 PM, Chris Plummer wrote:
>> Hi David,
>>
>> On 9/13/17 5:12 PM, David Holmes wrote:
>>> Hi Chris,
>>>
>>> On 14/09/2017 8:23 AM, Chris Plummer wrote:
>>>> I could use one more reviewer.
>>>
>>> Generally this seems okay to me.
>>>
>>> One query though ... in createAttachFile don't you need to alter the 
>>> tmpdir using part in a similar manner to how findSocketFile was 
>>> modified?
>> The fix in findSocketFile is not just to make sure the client uses 
>> the correct pid in the .java_pid file files, but also (as you point 
>> out) to make sure that the client properly references the target 
>> jvm's tmp directory when accessing the .java_pid file. findSocketFile 
>> is a little 
>
> I presume you mean createAttachFile there.
Yes.
>
>> different. You still have to map to the proper from pid to ns_pid 
>> when referencing the .attach_pid file, but you don't have the /tmp 
>> mount point differences to deal with. /proc/<pid>/cwd should work 
>> even if the pid is for a docker. You don't even have to map to the 
>> pid as the docker sees it. /proc/<pid>/cwd from the client's POV 
>> should be the same as /proc/<ns_pid>/cwd from the target JVM's POV.
>
> Sorry but I don't follow. If findSocketFile has to look in 
> /proc/<pid>/root/<tmpdir> for the socket file, why does the 
> createAttachFile not also have to write the attach file into 
> /proc/<pid>/root/<tmpdir> ?? In both cases it needs to find the tmpdir 
> of the target process.
Fortunately I have some old printlns that might help:

***getNamespacePid - ns_pid: 125
***findSocketFile - f: /proc/24445/root/tmp/.java_pid125
***createAttachFile - path: /proc/24445/cwd/.attach_pid125

So this is a case where the real pid is 24445, but the namespace pid in 
the docker is 125. The docker can (and does) reference 
/tmp/.java_pid125, but the client needs to reference 
/proc/24445/root/tmp/.java_pid125 to get to the same file. For 
.attach_pid125, the client can get to it through 
/proc/24445/cwd/.attach_pid125, and the docker process will look in cwd 
for the file. This is done in AttachListener::is_init_trigger().

BTW, comments like the following are no longer correct due to JDK-7132199:

     // "/tmp" is used as a global well-known location for the files
     // .java_pid<pid>. and .attach_pid<pid>. It is important that this
     // location is the same for all processes, otherwise the tools
     // will not be able to find all Hotspot processes.
     // Any changes to this needs to be synchronized with HotSpot.
     private static final String tmpdir = "/tmp";

So now .attach_pid<pid> is always created in cwd as you can see in 
createAttachFile(), although AttachListener::is_init_trigger() does 
check tmp, but only after cwd.

thanks,

Chris
>
> Thanks,
> David
>
>>>
>>> Minor note - you can collapse your catch blocks into 1 using 
>>> something like
>>>
>>> ������� } catch (NumberFormatException | IOException x) {
>>> ������������ throw new AttachNotSupportedException("Unable to parse 
>>> namespace");
>>> ������� }
>> I'll make that change.
>>
>> thanks,
>>
>> Chris
>>>
>>> Cheers,
>>> David
>>>> thanks,
>>>>
>>>> Chris
>>>>
>>>> On 9/11/17 8:03 PM, Chris Plummer wrote:
>>>>> Ok, I will. Thanks.
>>>>>
>>>>> Chris
>>>>>
>>>>> On 9/11/17 6:13 PM, serguei.spitsyn at oracle.com wrote:
>>>>>> Hi Chris,
>>>>>>
>>>>>> This looks good to me.
>>>>>>
>>>>>> I'm not sure if all the nsk.aod and the AttachOnDemand tests from
>>>>>> the nsk.jvmti are run in the hotspot tier1, 2, and 3 tests.
>>>>>> It makes sense to double-check it.
>>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Serguei
>>>>>>
>>>>>>
>>>>>> On 9/10/17 20:34, Chris Plummer wrote:
>>>>>>> [re-sending - sent to wrong alias first time]
>>>>>>>
>>>>>>> Hello,
>>>>>>>
>>>>>>> Please review the following:
>>>>>>>
>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8179498
>>>>>>> http://cr.openjdk.java.net/~cjplummer/8179498/webrev.00/webrev_jdk/
>>>>>>>
>>>>>>> The CR has the relevant details. Some previous discussions can 
>>>>>>> be found here:
>>>>>>>
>>>>>>> http://mail.openjdk.java.net/pipermail/serviceability-dev/2017-April/021237.html 
>>>>>>>
>>>>>>> http://mail.openjdk.java.net/pipermail/serviceability-dev/2017-May/021249.html 
>>>>>>>
>>>>>>> http://mail.openjdk.java.net/pipermail/serviceability-dev/2017-August/021679.html 
>>>>>>>
>>>>>>>
>>>>>>> Testing with docker has been limited to just making sure jcmd 
>>>>>>> now works with the docker setup I was provided. I currently 
>>>>>>> don't see how we can run our existing tests in a way that would 
>>>>>>> test the docker support without doing some rewriting of the tests.
>>>>>>>
>>>>>>> I also ran all our hotspot tier1, 2, and 3 tests, along with 
>>>>>>> jdk/test/tools and jdk/test/sun/tools tests to make sure 
>>>>>>> existing functionality is not broken with these changes.
>>>>>>>
>>>>>>> thanks,
>>>>>>>
>>>>>>> Chris
>>>>>>
>>>>>
>>>>
>>
>>