Andrew,

This patch prevents execution of hvc_write() and hvc_hangup() after the
tty layer has executed a final hvc_close() against a device.  This patch
provides a better method than was previously used.  tty->driver_data is
no longer invalidated so we'll no longer get oopses when the tty layer
allows late hangup() and write() operations.

changelog
-------------------------------------------------------------------------
drivers/char/hvc_console.c

-Removed silly tty->driver_data = NULL; from hvc_close which prevents
possible oops in hvc_write() and hvc_hangup() due to improperly acting
ldisc close ordering.

-Added hp->count <= 0 check to hvc_write() and hvc_hangup() to prevent
execution of these function after hvc_close() has been invoked by the
tty layer.  Same tty ldisc issues as above are the reason.

-Added some comments to clarify the situation.

-Awaiting a forth coming patch from Alan Cox which should clean up the
close ordering and prevent the late hangup and write ops from happening.

Thanks,
Ryan S. Arnold
IBM Linux Technology Center