From owner-freebsd-questions@FreeBSD.ORG  Mon Mar 23 18:32:13 2015
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Date: Mon, 23 Mar 2015 11:32:12 -0700 (MST)
From: BBlister <bblister@gmail.com>
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Subject: Re: Un-kill-able process hang at umtxpi state with 100% cpu
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The process named c1 in the home directory of that student, had an
accompanied c1.c file that actually is one that spawn many working pthreads
and synchronizes them at the end. I executed by a normal user
and nothing strange happened.

So I assume that was a rare timing issue/race condition that triggered this
error. 
I will have to upgrade of course to 9.3 in order to rule out old problems.

So, the takeaway of this is that sometimes when kill -KILL does not work,
kill -STOP may do the job :)



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