ssh child process hangs (Call proc.terminate before proc.wait when possible?)

[dobey]

Sometimes, it is possible for the child ssh process to seemingly be stuck waiting for something, causing the parent to hang in wait. The fix applied for bug #659590 however, does not fix this. But calling proc.terminate before proc.wait, does cause the problem to go away. It seems safe to terminate the process at this point, since the stdout/stdin have already been closed.

[Martin Pool (mbp)]

Thanks for the report.

Just killing the subprocess seems like kind of a big hammer, and one I'd rather not apply until we either know the problem, or we have consciously given up on understanding it.

If you can reproduce this can you please tell us

1- what strace shows that bzr and the child are doing
2- ditto 'ps o pid,wchan $SSH_PID'
3- 'lsof -p $SSH_PID'
4- the C-level backtrace of the child (attach using gdb, etc.)

You may need to run some of them as root to get around current security restrictions.

[Max Bowsher (maxb)]

I'd go so far as to say that bzr should NOT WAIT for ssh children to exit. Consider the use of ssh in ControlMaster auto mode. A ssh child invoked by bzr may remain active managing a multiplexed connection long after bzr itself is done with the channels being run over that process's stdin/out.

[Martin Pool (mbp)]

On 9 December 2010 21:53, Max Bowsher <email address hidden> wrote:
> I'd go so far as to say that bzr should NOT WAIT for ssh children to
> exit. Consider the use of ssh in ControlMaster auto mode. A ssh child
> invoked by bzr may remain active managing a multiplexed connection long
> after bzr itself is done with the channels being run over that process's
> stdin/out.

I'm a bit surprised to discover this is true. I had assumed that the
opportunistic master would detach itself once the original command
completed, but apparently not. So I agree, yes, we shouldn't wait.
We could do a non-blocking check whether they have exited but even
that may be of limited value.

--
Martin

[Launchpad Janitor (janitor)]

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