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Sender: Alexander Motin <mavbsd@gmail.com>
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Date: Wed, 14 Dec 2011 00:43:22 +0200
From: Alexander Motin <mav@FreeBSD.org>
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To: Chuck Tuffli <chuck@tuffli.net>
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Cc: freebsd-scsi <freebsd-scsi@freebsd.org>
Subject: CAM locking question
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Hi.

 > As an experiment, I added CAM_SIM_LOCK/CAM_SIM_UNLOCK around the
 > TAILQ_INSERT_TAIL() in xpt_done(), and what was a reliable hang after
 > a minute or two hasn't shown up in an hour.

There is no assertion, but in all cases I remember xpt_done() called 
while holding SIM lock. Adding another CAM_SIM_LOCK/CAM_SIM_UNLOCK 
should cause lock recursion and panic, if kernel built with INVARIANTS.

-- 
Alexander Motin