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Re: CVS commit: src/sys/kern
On 15 Apr 2014, at 20:18, Taylor R Campbell
> 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?
Kpause() registers a callout and sleeps.
On the next clock tick the softclk thread calls timer_intr() which
wants the proc_lock. Now we successfully stopped all softclk threads.
The callout for kpause() will not fire -> deadlock/
J. Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig
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