mgr: fixes python error handling

[rjfd]

The current handle_pyerror function implementation relies in the
traceback.format_exception_only python function to format the
exception object. The problem is that this python function might also
raise an exception. This commit fixes it by enclosing that python
function call in try...catch block.

Fixes: http://tracker.ceph.com/issues/23406

Signed-off-by: Ricardo Dias rdias@suse.com

[sebastian-philipp]

s/format_exception_only/format_exception/g

[rjfd]

fixed

lgtm

[jcsp]

Out of curiousity, what was the exception that format_exception_only was throwing?

[tserong]

Out of curiousity, what was the exception that format_exception_only was throwing?

I was wondering the same thing. Do we care that this piece is effectively invisible?

[rjfd]

@jcsp @tserong I'm investigating a bit further the root cause of the problem to answer your question.

[rjfd]

@jcsp @tserong

First of all, this problem only occurs when running ceph-mgr daemon with python 3.
After investigating the root cause of the problem I found that:

• the exception thrown while executing traceback.format_exception is only thrown when handling an exception raised by the C python API, for instance handling an execption raised while executing PyArg_ParseTuple.
• (according to Failure in new dreload tests under Python 3.2 ipython/ipython#1626, and I confirmed that it was the case) apparently some exceptions' value generated by the C python API when raising an exception, have the str type instead of being an object of a class that subclasses BaseException. This is the cause of the exception thrown by traceback.format_exception with the following message: 'str' object has no attribute '__cause__'.

I updated the PR fix to show the exception type, plus exception value, when the traceback.format_exception raises an exception.

For instance, when calling the ceph dashboard set-login-credentials ... with the implementation described in the tracker issue, we now get the following message:
TypeError: ceph_config_set() argument 2 must be str or None, not bytes

[rjfd]

@tserong removed the two unused variables from the code

[rjfd]

jenkins retest this please

[rjfd]

jenkins retest this please