deadlock between g_event and a thread on removing a device.

[Kohji Okuno]

Hi,

When I removed a device (ex. /dev/da0), I have encounterd a
dead-lock between ``g_event'' thread and a thread that is opening
device file (I call this thread as A).

Would you refer the following?

When the device is removed between dev_refthread() and g_dev_open(),
thread A incremented dev->si_threadcount, but can't acquire
topology_lock.

On the other hand, g_event is waiting to set dev->si_threadcount to 0
with topology_lock.

Regards,
 Kohji Okuno


<<< Thread A >>>
...
devfs_open()
{
  ...
  dsw = dev_refthread(dev, &ref); <= increment dev->si_threadcount
  ...
  error = dsw->d_open(...);       <= call g_dev_open()
  ...
  dev_relthread(dev, ref);        <= decrement dev->si_threadcount
}

g_dev_open()
{
  ...
  g_topology_lock();              <= Thread A couldn't acquire 
  ...                                topology_lock.
}

<<< g_event >>>
g_run_events()
{
   ...
   g_topology_lock();             <= g_event acuired topology_lock here.
   ...
   one_event()
   ...
}

one_event()
g_orphan_register()
g_dev_orphan()
destroy_dev()
destroy_dev()
destroy_devl()
{
  ...
  while (dev->si_threadcount != 0) { <= this count was incremented by Thread A
    /* Use unique dummy wait ident */
    msleep(&csw, &devmtx, PRIBIO, "devdrn", hz / 10);
  }
  ...
}