Re: CVS commit: src/sys/kern

[Taylor R Campbell <campbell+netbsd-source-changes-d%mumble.net@localhost>]

   Date: Tue, 15 Apr 2014 09:50:45 +0000
   From: Juergen Hannken-Illjes <hannken%NetBSD.org@localhost>

   Fix a deadlock where one thread exits, enters fstrans_lwp_dtor()
   and wants fstrans_lock.  This thread holds the proc_lock.

This sounds fishy.  lwp_exit does not hold proc_lock while calling
lwp_finispecific, so there are no invariants covered by proc_lock that
the lwp_specific destructors can rely on.  I'm inclined to say that it
is a bug for exit1 to hold proc_lock when it calls lwp_finispecific
(and proc_finispecific).  Can we just release it before and re-acquire
it after calling lwp/proc_finispecific?

   Another thread holds fstrans_lock and runs pserialize_perform().
   As the first thread holds the proc_lock, timeouts are blocked and
   the second thread blocks forever in kpause().

This also sounds fishy.  How does T1's holding proc_lock cause T2 to
block forever in kpause?  I think I'm missing something in this
analysis.  kpause doesn't take proc_lock, does it?