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

Chris Plummer chris.plummer at oracle.com
Fri Sep 15 04:19:03 UTC 2017 

On 9/14/17 9:56 AM, Chris Plummer wrote:
> On 9/14/17 1:45 AM, David Holmes wrote:
>> On 14/09/2017 5:53 PM, Dmitry Samersoff wrote:
>>> Chris,
>>>
>>>> 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.
>>>
>>>> ***getNamespacePid - ns_pid: 125
>>>> ***findSocketFile - f: /proc/24445/root/tmp/.java_pid125
>>>> ***createAttachFile - path: /proc/24445/cwd/.attach_pid125
>>>
>>> Could we always use tmp ?
>>>
>>> IMHO cwd is not a right choice for such kind of files, it should be
>>> either $HOME or tmp.
>>
>> And we hardwired /tmp and stopped using cwd under
>>
>> https://bugs.openjdk.java.net/browse/JDK-7132199
>>
>> So I'm a bit confused as to how this has evolved back into using cwd. ??
> Yeah, I had this backwards with my earlier comment. Before JDK-7132199 
> we actually do it the way we do now, trying cwd first, and then tmp if 
> it fails. JDK-7132199 made it only use tmp, but only for 
> findSocketFile(). createAttachFile() still tries cwd first and then 
> tmp, and I see nothing in the history to indicate this was ever 
> changed, other than to force the location of tmp to /tmp with 
> JDK-6950927.
>
> So the question is do we get rid of the cwd support and always use 
> tmp? If yes, I think it's best not to do that as part of this CR. I'd 
> rather just add the docker /tmp support to createAttachFile() now, and 
> have a separate CR deal with removing all cwd support (or maybe even 
> push changes for it before the docker support fix).
Here's an updated webrev with the tmpdir fix in createAttachFile():

http://cr.openjdk.java.net/~cjplummer/8179498/webrev.02/webrev_jdk/

I ran all the same tests again, including testing with docker. To make 
sure it was hitting the tmpdir code, I forced the cwd code to error out 
by making it use cwdX instead.

There are also two other changes to fix an issue I noticed when you 
provide a bad pid. You are suppose to get an error message like this:

java.io.IOException: No such process
     at jdk.attach/sun.tools.attach.VirtualMachineImpl.sendQuitTo(Native 
Method)
     at 
jdk.attach/sun.tools.attach.VirtualMachineImpl.<init>(VirtualMachineImpl.java:80)
     at 
jdk.attach/sun.tools.attach.AttachProviderImpl.attachVirtualMachine(AttachProviderImpl.java:58)
     at 
jdk.attach/com.sun.tools.attach.VirtualMachine.attach(VirtualMachine.java:207)
     at jdk.jcmd/sun.tools.jcmd.JCmd.executeCommandForPid(JCmd.java:114)
     at jdk.jcmd/sun.tools.jcmd.JCmd.main(JCmd.java:98)

However, I was seeing the following due to the docker related changes:

java.nio.file.NoSuchFileException: /proc/7777/status
     at 
java.base/sun.nio.fs.UnixException.translateToIOException(UnixException.java:92)
     at 
java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:111)
     at 
java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:116)
     at 
java.base/sun.nio.fs.UnixFileSystemProvider.newByteChannel(UnixFileSystemProvider.java:215)
     at java.base/java.nio.file.Files.newByteChannel(Files.java:369)
     at java.base/java.nio.file.Files.newByteChannel(Files.java:415)
     at 
java.base/java.nio.file.spi.FileSystemProvider.newInputStream(FileSystemProvider.java:384)
     at java.base/java.nio.file.Files.newInputStream(Files.java:154)
     at java.base/java.nio.file.Files.newBufferedReader(Files.java:2830)
     at java.base/java.nio.file.Files.readAllLines(Files.java:3260)
     at 
jdk.attach/sun.tools.attach.VirtualMachineImpl.getNamespacePid(VirtualMachineImpl.java:334)
     at 
jdk.attach/sun.tools.attach.VirtualMachineImpl.<init>(VirtualMachineImpl.java:71)
     at 
jdk.attach/sun.tools.attach.AttachProviderImpl.attachVirtualMachine(AttachProviderImpl.java:58)
     at 
jdk.attach/com.sun.tools.attach.VirtualMachine.attach(VirtualMachine.java:207)
     at jdk.jcmd/sun.tools.jcmd.JCmd.executeCommandForPid(JCmd.java:114)
     at jdk.jcmd/sun.tools.jcmd.JCmd.main(JCmd.java:98)

I fixed getNamespacePid() to validate that /proc/<pid>/status exists 
before trying to process it. If it doesn't, it just returns pid rather 
than trying to find ns_pid. However, that led to:

java.io.IOException: No such file or directory
     at java.base/java.io.UnixFileSystem.createFileExclusively(Native 
Method)
     at java.base/java.io.File.createNewFile(File.java:1024)
     at 
jdk.attach/sun.tools.attach.VirtualMachineImpl.createAttachFile(VirtualMachineImpl.java:300)
     at 
jdk.attach/sun.tools.attach.VirtualMachineImpl.<init>(VirtualMachineImpl.java:78)
     at 
jdk.attach/sun.tools.attach.AttachProviderImpl.attachVirtualMachine(AttachProviderImpl.java:58)
     at 
jdk.attach/com.sun.tools.attach.VirtualMachine.attach(VirtualMachine.java:207)
     at jdk.jcmd/sun.tools.jcmd.JCmd.executeCommandForPid(JCmd.java:114)
     at jdk.jcmd/sun.tools.jcmd.JCmd.main(JCmd.java:98)

This is because createAttachFile() first tried to create the file in 
/proc/<pid>/cwd, and after that failed with IOException (which is 
caught), it tried in /proc/<pid>/root/tmp, which fails with the above 
uncaught IOException. I changed the code to only try 
/proc/<pid>/root/tmp if pid != ns_pid (which means either it is a docker 
situation and the pid is valid). Otherwise it reverts to the old 
behavior just using /tmp.

thanks,

Chris
>
> thanks,
>
> Chris
>>
>> David
>>
>>
>>> -Dmitry
>>>
>>> On 14.09.2017 07:15, Chris Plummer wrote:
>>>> 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
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>
>>>>>>
>>>>
>>>>
>>>
>>>
>
>

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