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Date: Tue, 30 Dec 2014 10:48:31 +0100
From: Hans Petter Selasky <hps@selasky.org>
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To: Chris H <bsd-lists@bsdforge.com>, Warren Block <wblock@wonkity.com>
Subject: Re: HEADS UP: Enabling vt(4) by default
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Hi,

I just had a quick look at "vt_core.c" with regard to callouts. And have 
the following comments:

1) Make sure callout_reset(), callout_schedule() and callout_stop() is 
always called locked. When no lock is specified, that means Giant!

2) callout_drain() must have an unlocked sleeping context, else use 
callout_stop() with the mutex specified in callout_init_mtx() to get 
atomicity.

For now adding MTX_RECURSE to "mtx_init(&main_vd->vd_lock, "vtdev", 
NULL, MTX_DEF | MTX_RECURSE)" solved my problem temporarily, because 
callout_drain() tried to get the vd_lock, which was already taken.

--HPS