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Posted to dev@mina.apache.org by "Mike Pomraning (JIRA)" <ji...@apache.org> on 2015/11/06 18:45:11 UTC
[jira] [Commented] (SSHD-557) MINA SSHD deadlocks upon multiple
concurrent HTTP downloads over locally-forwarded ports
[ https://issues.apache.org/jira/browse/SSHD-557?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14994061#comment-14994061 ]
Mike Pomraning commented on SSHD-557:
-------------------------------------
I have tested the SSHD-565 timeout, but it's no help by itself as the workers re-enter the {{wait}} too quickly. An indefinite wait becomes a busier indefinite wait. We can reproduce this with just a few sessions.
Now, I'd like to persuade you that increasing the workers is an inappropriate fix, too. (As an aside, I think [~sgardner] was suggesting a dedicated thread that was "read only" on the sessions, and thus could not itself get stuck in {{waitForSpace}}.)
Essentially, we have a multiplexing multithreaded model where it is possible for every worker thread to enter an indefinitely blocking wait and thus starve all clients, even those with "healthy" sessions. I am sympathetic to your suggestion of capacity tuning, and I see this as an issue of _correctness_ under any load rather than _performance_ under heavy load.
In a single event-driven thread multiplexing many clients — maybe Netty or twisted python or perl POE — it's not correct to block indefinitely on any one client. Saying that we need N+1 threads, where N is the number of clients, defeats the purpose of event-driven multiplexed client sessions in the first place.
A fix might be to put the "stuck" session in their own set, off to the side, and leave them there until incoming data suggest their window can be resized.
> MINA SSHD deadlocks upon multiple concurrent HTTP downloads over locally-forwarded ports
> ----------------------------------------------------------------------------------------
>
> Key: SSHD-557
> URL: https://issues.apache.org/jira/browse/SSHD-557
> Project: MINA SSHD
> Issue Type: Bug
> Affects Versions: 0.14.0, 1.0.0
> Environment: Fedora 21, kernel 3.17.4-301, OpenJDK 1.8.0_51-b16
> Reporter: Sam Gardner
> Assignee: Goldstein Lyor
> Labels: sshd
> Fix For: 1.1.0
>
> Attachments: AbstractUserAuth.java, setup-tunnels-remote.sh, setup-tunnels.sh, ssh-load-remote.sh, ssh-load.sh, sshd-core-0.14.0-jar-with-dependencies.jar, sshd-core-1.0.0-jar-with-dependencies.jar
>
>
> SSHD-Core 1.0.0 deadlocks when multiple concurrent downloads are in progress over ChannelOutputStreams
> In both Mina-SSHD 0.14.0 and 1.0.0 the server will become deadlocked if multiple concurrent downloads are started over a locally-forwarded TCP socket. In this state the process is still alive and client connections stay open, but no data can be transmitted and new connections will not be accepted - when inspected via telnet, the SSH port will not even return a banner.
> Inspection of the hung process using the {{jstack}} tool shows that each NIO worker thread is in the following state: {noformat}
> "sshd-SshServer[36f6e879]-nio2-thread-4" #14 daemon prio=5 os_prio=0 tid=0x00007f219c009000 nid=0x34c6 in Object.wait() [0x00007f21c8439000]
> java.lang.Thread.State: WAITING (on object monitor)
> at java.lang.Object.wait(Native Method)
> - waiting on <0x00000000d799f9b0> (a org.apache.sshd.common.channel.Window)
> at java.lang.Object.wait(Object.java:502)
> at org.apache.sshd.common.channel.Window.waitForSpace(Window.java:175)
> - locked <0x00000000d799f9b0> (a org.apache.sshd.common.channel.Window)
> at org.apache.sshd.common.channel.ChannelOutputStream.flush(ChannelOutputStream.java:126)
> - locked <0x00000000d799fa68> (a org.apache.sshd.common.channel.ChannelOutputStream)
> at org.apache.sshd.server.forward.TcpipServerChannel$1.messageReceived(TcpipServerChannel.java:156)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:220)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> at java.nio.channels.AsynchronousSocketChannel.read(AsynchronousSocketChannel.java:420)
> at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:247)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:224)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> at java.nio.channels.AsynchronousSocketChannel.read(AsynchronousSocketChannel.java:420)
> at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:247)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:224)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> at java.nio.channels.AsynchronousSocketChannel.read(AsynchronousSocketChannel.java:420)
> at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:247)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:224)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> at java.nio.channels.AsynchronousSocketChannel.read(AsynchronousSocketChannel.java:420)
> at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:247)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:224)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> at java.nio.channels.AsynchronousSocketChannel.read(AsynchronousSocketChannel.java:420)
> at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:247)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:224)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> at java.nio.channels.AsynchronousSocketChannel.read(AsynchronousSocketChannel.java:420)
> at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:247)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:224)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> at java.nio.channels.AsynchronousSocketChannel.read(AsynchronousSocketChannel.java:420)
> at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:247)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:224)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> at java.nio.channels.AsynchronousSocketChannel.read(AsynchronousSocketChannel.java:420)
> at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:247)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:224)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
> at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:553)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:276)
> at sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:297)
> at java.nio.channels.AsynchronousSocketChannel.read(AsynchronousSocketChannel.java:420)
> at org.apache.sshd.common.io.nio2.Nio2Session.doReadCycle(Nio2Session.java:247)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:224)
> at org.apache.sshd.common.io.nio2.Nio2Session$2.onCompleted(Nio2Session.java:212)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler$1.run(Nio2CompletionHandler.java:34)
> at java.security.AccessController.doPrivileged(Native Method)
> at org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:31)
> at sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> at sun.nio.ch.Invoker$2.run(Invoker.java:218)
> at sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:112)
> at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> at java.lang.Thread.run(Thread.java:745)
> {noformat}
> These are the steps to reproduce:
> # Start up approximately 200 separate SSH sessions with one local forward to an HTTP server:
> {{ssh -N -LXXXXX:<HTTP_SERVER>:80 account@<MINA_SSHD_SERVER>}}
> ## To simplify this process, I modified [org.apache.sshd.server.auth.AbstractUserAuth|^AbstractUserAuth.java] to always accept requests - this makes it possible to create the sessions on the same client (though I've also reproduced this on separate clients as well).
> ## This [script|^setup-tunnels.sh] will setup the client sessions as background processes
> # With the above sessions alive and backgrounded, fetch large files concurrently from the HTTP server over multiple forwarded ports:
> {{wget http://localhost:XXXXX/hugefile}}
> ## This [script|^ssh-load.sh] will start {{wget}} downloads in the above manner.
> # After a time, the {{wget}} downloads will stop progressing, and inspection of the SSH server process via {{jstack <PID>}} will show each of the {{nio2-thread-[0-9]}} threads in the deadlocked state.
> Note: I previously filed SSHD-539 on this, and have since reproduced it on vanilla MINA SSHD-Core without our proprietary modifications and running outside of Tomcat.
> The JAR files I used to reproduce are attached to this ticket as well.
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