usbdevfs mount 2x, umount 1x

[Randy Dunlap <randy.dunlap@intel.com>]

[I reported this a couple of months back.  Got no
feedback on it.  If it's just a DDT (don't do that)
or a user error, please say so.]

Summary:  After I mount usbdevfs 2 times, and umount it
1 time, the usbcore module use count prevents it from
being rmmod-ed.

This is test12-pre2.


1.  Start by loading usbcore and uhci modules:
 
[root@dragon rdunlap]# lsmod
Module                  Size  Used by
uhci                   18848   0  (unused)
usbcore                50656   0  [uhci]

and the /proc/bus/usb mount point is empty:

[rdunlap@dragon rdunlap]$ ls -l /proc/bus/usb
total 0

2.  I enter "mount usb", which uses this entry
from /etc/fstab:
usb    /proc/bus/usb    usbdevfs defaults,user  0 0

'mount' then tells me (usb line extracted):

usb on /proc/bus/usb type usbdevfs (rw,noexec,nosuid,nodev)

and 'lsmod' tells me:

[root@dragon rdunlap]# lsmod
Module                  Size  Used by
uhci                   18848   0  (unused)
usbcore                50656   1  [uhci]

3.  Some time passes.  I mount usbdevfs again, by entering:

[root@dragon rdunlap]# mount -t usbdevfs usbdevfs /proc/bus/usb

'lsmod' now tells me:

[root@dragon rdunlap]# lsmod
Module                  Size  Used by
uhci                   18848   0  (unused)
usbcore                50656   2  [uhci]

and 'mount' tells me:

usb on /proc/bus/usb type usbdevfs (rw,noexec,nosuid,nodev)
usbdevfs on /proc/bus/usb type usbdevfs (rw)

4.  I 'umount usbdevfs'.  Now 'lsmod' tells me:

[root@dragon rdunlap]# umount usbdevfs
[root@dragon rdunlap]# lsmod
Module                  Size  Used by
uhci                   18848   0  (unused)
usbcore                50656   1  [uhci]

and 'mount' shows no usb or usbdevfs entries listed.

Now I rmmod uhci and 'lsmod' tells me:

[root@dragon rdunlap]# rmmod uhci
[root@dragon rdunlap]# lsmod
Module                  Size  Used by
usbcore                50656   1 

and I can't rmmod usbcore.  The /proc/bus/usb mount
point is still populated and the 'drivers' file
contains correct data:

[rdunlap@dragon rdunlap]$ ls -l /proc/bus/usb
total 0
-r--r--r--   1 root     root            0 Nov 29 16:17 devices
-r--r--r--   1 root     root            0 Nov 29 16:17 drivers

[rdunlap@dragon rdunlap]$ cat /proc/bus/usb/drivers 
         hub
         usbdevfs
[rdunlap@dragon rdunlap]$


So is this just a case of root being able to shoot self
in foot or a proc-fs or module counter problem? 

Notes:
1. Reversing the order of steps 3 and 4 gives the
same results.
2. Changing the device name in
'mount -t usbdevfs usbdevfs /proc/bus/usb' to be
'mount -t usbdevfs usbfs   /proc/bus/usb' gives the
same results (when followed by 'umount usbfs').

Thanks,
~Randy
-- 
_______________________________________________
|randy.dunlap_at_intel.com        503-677-5408|
|NOTE: Any views presented here are mine alone|
|& may not represent the views of my employer.|
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