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Date: Thu, 19 Feb 2004 10:05:21 +0200
From: Andrey Simonenko <simon@comsys.ntu-kpi.kiev.ua>
To: Jerry Toung <jtoung@arc.nasa.gov>
Message-ID: <20040219080521.GA439@pm514-9.comsys.ntu-kpi.kiev.ua>
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cc: hackers <freebsd-hackers@freebsd.org>
Subject: Re: locking against myself
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On Wed, Feb 18, 2004 at 11:52:26AM -0800, Jerry Toung wrote:
> Hello hackers,
> I am constantly getting the following message when I run my KLD:
> 
> panic: lockmgr: locking against myself
> Debugger("panic")
> Stopped at		Debugger+0x54:		xchgl		%ebx,in_Debugger.0
> db>
> 
> What could possibly cause this?
> It seem to say that I'm locking an already locked variable.
> 

Hello Jerry,

According to kern/kern_lock.c:lockmgr() your proc/thread already
has an exclusive lock and it tries to obtain a recursive exclusive
lock and lock doesn't have LK_CANRECURSE flag (also you allow to
sleep in lockmng()).

This is documented in lock(9) manual page:

       LK_EXCLUSIVE    Acquire an exclusive lock.  If an exclusive
		       lock is already held, and LK_CANRECURSE is not
		       set, the system will panic(9).