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Date:      Thu, 06 Aug 2020 14:33:09 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 248500] cam_sim_free() sleeping forever
Message-ID:  <bug-248500-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=248500

            Bug ID: 248500
           Summary: cam_sim_free() sleeping forever
           Product: Base System
           Version: CURRENT
          Hardware: amd64
                OS: Any
            Status: New
          Keywords: cam
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: bz@FreeBSD.org
                CC: bsdimp@FreeBSD.org

Hi,

I have a system with a locked USB because cam_sim_free() seems to sleep forever
(at least 24 hours by now):

# procstat -akk | grep -i usb
   15 100045 usb                 usbus0              mi_switch+0xc1
_cv_wait+0xf2 usb_process+0x101 fork_exit+0x7e fork_trampoline+0xe
   15 100046 usb                 usbus0              mi_switch+0xc1
_cv_wait+0xf2 usb_process+0x101 fork_exit+0x7e fork_trampoline+0xe
   15 100047 usb                 usbus0              mi_switch+0xc1
_cv_wait+0xf2 usb_process+0x101 fork_exit+0x7e fork_trampoline+0xe
   15 100048 usb                 usbus0              mi_switch+0xc1
_sleep+0x1cb cam_sim_free+0x7e umass_detach+0xd8 device_detach+0x185
device_delete_child+0x15 usb_detach_device+0x18f usb_unconfigure+0x2b
usb_free_device+0x
11d uhub_explore+0x2ad usb_bus_explore+0x13e usb_process+0x13b fork_exit+0x7e
fork_trampoline+0xe
   15 100049 usb                 usbus0              mi_switch+0xc1
_cv_wait+0xf2 usb_process+0x101 fork_exit+0x7e fork_trampoline+0xe


0x2be is in cam_sim_free (/usr/src/head.svn/sys/cam/cam_sim.c:142).
137             if (sim->refcount > 0) {
138                     error = msleep(sim, mtx, PRIBIO, "simfree", 0);
139                     KASSERT(error == 0, ("invalid error value for
msleep(9)"));
140             }
141             KASSERT(sim->refcount == 0, ("sim->refcount == 0"));
142             if (sim->mtx == NULL)
143                     mtx_unlock(mtx);
144
145             if (free_devq)
146                     cam_simq_free(sim->devq);


What should wake us up in this case?  Was there a race somewhere?  Any ideas?

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