Re: Strange hanging bug in a simple milter

* Stephen Frost (sfrost(at)snowman(dot)net) wrote:
> * Andres Freund (andres(at)2ndquadrant(dot)com) wrote:
> > Hm. close_SSL() first does pqsecure_destroy() which will unset the
> > callbacks, and the count and then goes on to do X509_free() and
> > ENGINE_finish(), ENGINE_free() if either is used.
> >
> > It's not implausible that one of those actually needs locking. I doubt
> > engines play a role here, but, without having looked at the testcase,
> > X509_free() might be a possibility.
>
> Unfortunately, while I can still easily get the deadlock to happen when
> the hooks are reset, the hooks don't appear to ever get called when
> ssl_open_connections is set to zero. You have a good point about the
> additional SSL calls after the hooks are unloaded though, I wonder if
> holding the ssl_config_mutex lock over all of close_SSL might be more
> sensible..

I went ahead and moved the locks to be around all of close_SSL() and
haven't been able to reproduce the deadlock, so perhaps those calls are
the issue and what's happening is that another thread is dropping or
adding the hooks in a common place while the X509_free, etc, are trying
to figure out if they should be calling the locking functions or not,
but there's a race because there's no higher-level locking happening
around those.

Attached is a patch to move those and which doesn't deadlock for me.

Thoughts?

Thanks,

Stephen