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Date: Sun, 21 Dec 2014 15:43:17 +0100
From: Hans Petter Selasky <hps@selasky.org>
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To: Fabian Keil <freebsd-listen@fabiankeil.de>
Subject: Re: Panic after USB deadlock followed by kldunload umass.ko
References: <03fafb9a.529c7f26@fabiankeil.de> <5449119B.8090401@selasky.org>
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On 12/21/14 14:54, Fabian Keil wrote:
> #0  sched_switch (td=0xfffff80015ea0940, newtd=<value optimized out>, flags=<value optimized out>) at /usr/src/sys/kern/sched_ule.c:1940
> #1  0xffffffff805bbf91 in mi_switch (flags=260, newtd=0x0) at /usr/src/sys/kern/kern_synch.c:492
> #2  0xffffffff8060126a in sleepq_wait (wchan=0x0, pri=0) at /usr/src/sys/kern/subr_sleepqueue.c:631
> #3  0xffffffff805bb99d in _sleep (ident=<value optimized out>, lock=<value optimized out>, priority=<value optimized out>, wmesg=<value optimized out>, sbt=<value optimized out>, pr=<value optimized out>,
>      flags=<value optimized out>) at /usr/src/sys/kern/kern_synch.c:254
> #4  0xffffffff802a2548 in cam_sim_free (sim=0xfffff8004f9fa800, free_devq=1) at /usr/src/sys/cam/cam_sim.c:109

Because cam_sim_free() doesn't return, the USB subsystem belonging to 
that controller is somewhat blocked.

--HPS