abort() calls from messaging code

[Volker Lendecke]

On Thu, Jun 15, 2017 at 09:03:21AM -0700, Jeremy Allison via samba-technical wrote:
> On Thu, Jun 15, 2017 at 05:50:42PM +0200, Volker Lendecke wrote:
> > On Thu, Jun 15, 2017 at 08:45:30AM -0700, Jeremy Allison wrote:
> > > Arrrgggh. Sorry, this stuff is a black art :-(. Really sorry
> > > I didn't catch this in the 1828011317b review.
> > 
> > That's why we're putting so much effort into tevent_req and hiding
> > threads into a very dark corner. You only want to chase this kind of
> > problem very, very rarely in small pieces of code :-)
> 
> How did you catch it ? Race conditions are a nightmare to
> find and I'm interested in learning :-).

According to susv4 it's undefined behaviour to destroy a locked mutex.
So I tried to find out whether there are ways we could end up in that
situation. Took a bit, but it was mainly staring at code. There's very
few places where we lock/unlock that mutex, and so I finally found
that.

Volker

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