Hello, I see possible issues here, not sure if they still exist but I wanted to mention them:
the list-vm function might be slow on a loaded system (as it is a complex function). It’s not the best Situation if your diagnostic attempts are slow down in such a situation. Also in the past not all VMs might be recognized by the list function, a more targeted attach could still succeed. Is that addressed since the container-PID changes? In both cases a force option would help. Gruss Bernd Gruss Bernd -- http://bernd.eckenfels.net ________________________________ Von: serviceability-dev <serviceability-dev-boun...@openjdk.java.net> im Auftrag von gary.ad...@oracle.com Gesendet: Freitag, Februar 15, 2019 12:07 PM An: Thomas Stüfe; David Holmes; Chris Plummer Cc: OpenJDK Serviceability Betreff: Re: RFR: JDK-8149461: jmap kills process if non-java pid is specified in the command line Let me clarify a few things about the proposed fix. The VirtualMachine.list() mechanism is based on Java processes that are up and running. During VM startup when agent libraries are loaded, the fact is recorded in the filesystem that a Java process is eligible for an attach request. This is a much smaller list than scanning for all the running processes and works across all supported platforms. It also doesn't rely on fragile command line parsing to determine a Java launcher is used. I believe most of the reported hang situations are not for the first level information for pid and command line requests. I believe the hangs are due to the second level requests that actually attach to the process and issue a command to the running Java process. The overhead for the pid check should be relatively small. In a standalone command for a one time check at startup with 10's of Java processes. I know the documentation states the user is responsible for verifying with jps that a Java process pid or vmid is provided. But the cost of human error can be a terminated process. Selection by name also has some drawbacks when multiple copies of a command are running at the same time. Running "jcmd 0 ..." is the documented way to run a command on all running Java processes. May I count you as a reviewer on the current changeset? On 2/15/19 3:54 AM, Thomas Stüfe wrote: On Fri, Feb 15, 2019 at 3:26 AM David Holmes <david.hol...@oracle.com<mailto:david.hol...@oracle.com>> wrote: Gary, What is the overhead of doing the validation? How do we list VMs? Do we need to examine every running process to get the list of VMs? Wouldn't it be better to check the given process is a VM rather than checking all potential VM processes? I think this is a valid point. Listing VMs is normally quick (just use jcmd without any parms) but I have seen this fail or hang rarely in situations where I then still was able to talk to my VM via pid. I never investigated this but I would not like to be unable to connect to my VM just because some rogue VM mailfunctions. This would be an argument for the alternative I offered in my first answer - just use the proc file system or a similar mechanism to check only the pid you plan on sending sigquit to... I think there is an onus of responsibility on the user to provide a correct pid here, rather than trying to make this foolproof. Oh but it can happen quite easily. For example, by pulling up an older jcmd from your shell history and forgetting to modify the pid. Thank god for the command name argument option on jcmd, which I now use mostly. We also had a customer which tried to find all VMs on his machine by attempting to attach with jcmd to every process, killing them left and right :) ... Thomas Thanks, David On 15/02/2019 5:12 am, Gary Adams wrote: > The following commands present a similar kill process behavior: > jcmd > jinfo > jmap > jstack > > The following commands do not attach. > jstat sun.jvmstat.monitor.MonitorException "not found" > jps no pid arguments > > This update moves the checkJavaPid method into the > common/ProcessArgumentsMatcher.java > and applies the check before the pid is used for an attach operation. > > Revised webrev: http://cr.openjdk.java.net/~gadams/8149461/webrev.01/ > > On 2/14/19, 12:07 PM, Chris Plummer wrote: >> Hi Gary, >> >> What about the other tools that attach to a user specified process. Do >> they also have this issue? >> >> thanks, >> >> Chris >> >> On 2/14/19 8:35 AM, Gary Adams wrote: >>> There is an old reported problem that using jmap on a process that is >>> not running >>> Java could cause the process to terminate. This is due to the SIGQUIT >>> used >>> when attaching to the process. >>> >>> It is a fairly simple operation to validate that the pid matches one >>> of the known >>> running Java processes using VirtualMachine.list(). >>> >>> Issue: https://bugs.openjdk.java.net/browse/JDK-8149461 >>> >>> Proposed fix: >>> >>> diff --git a/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java >>> b/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java >>> --- a/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java >>> +++ b/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java >>> @@ -1,5 +1,5 @@ >>> /* >>> - * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All >>> rights reserved. >>> + * Copyright (c) 2005, 2019, 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 >>> @@ -30,6 +30,7 @@ >>> import java.io.InputStream; >>> import java.io<http://java.io>.UnsupportedEncodingException; >>> import java.util.Collection; >>> +import java.util.List; >>> >>> import com.sun.tools.attach.VirtualMachine; >>> import com.sun.tools.attach.VirtualMachineDescriptor; >>> @@ -125,6 +126,10 @@ >>> private static void executeCommandForPid(String pid, String >>> command, Object ... args) >>> throws AttachNotSupportedException, IOException, >>> UnsupportedEncodingException { >>> + // Before attaching, confirm that pid is a known Java process >>> + if (!checkJavaPid(pid)) { >>> + throw new AttachNotSupportedException(); >>> + } >>> VirtualMachine vm = VirtualMachine.attach(pid); >>> >>> // Cast to HotSpotVirtualMachine as this is an >>> @@ -196,6 +201,19 @@ >>> executeCommandForPid(pid, "dumpheap", filename, liveopt); >>> } >>> >>> + // Check that pid matches a known running Java process >>> + static boolean checkJavaPid(String pid) { >>> + List<VirtualMachineDescriptor> l = VirtualMachine.list(); >>> + boolean found = false; >>> + for (VirtualMachineDescriptor vmd: l) { >>> + if (vmd.id<http://vmd.id>().equals(pid)) { >>> + found = true; >>> + break; >>> + } >>> + } >>> + return found; >>> + } >>> + >>> private static void checkForUnsupportedOptions(String[] args) { >>> // Check arguments for -F, -m, and non-numeric value >>> // and warn the user that SA is not supported anymore >> >> >
