From owner-freebsd-stable@freebsd.org  Thu Nov 12 05:09:49 2015
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Subject: Re: Unkillable process in STOP state
To: Slawa Olhovchenkov <slw@zxy.spb.ru>, freebsd-stable@freebsd.org
References: <20151112001249.GI48728@zxy.spb.ru>
From: Eugene Grosbein <eugen@grosbein.net>
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Date: Thu, 12 Nov 2015 12:09:26 +0700
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On 12.11.2015 07:12, Slawa Olhovchenkov wrote:
> I have amd64, STABLE r288167.

>   PID    TID COMM             TDNAME           CPU  PRI STATE   WCHAN    
> kill -STOP don't have effect.
> gdb can't be attached.

That is expected, STOP-ed process cannot do anything, can't even die.
Use "kill -KILL", then "kill -CONT", so the KILL signal could be delivered and do the job.