------------[ cut here ]------------
WARNING: at /build/buildd/linux-2.6.38/fs/inode.c:1401 iput_final+0x1d0/0x1e0()
Hardware name: VirtualBox
Modules linked in: nls_utf8 isofs binfmt_misc vboxsf snd_intel8x0 snd_ac97_codec ac97_bus snd_pcm snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq snd_timer snd_seq_device ppdev parport_pc vboxguest psmouse snd joydev soundcore snd_page_alloc serio_raw i2c_piix4 lp parport usbhid hid ahci e1000 libahci
Pid: 2153, comm: mount.vboxsf Tainted: G        W   2.6.38-7-generic #39-Ubuntu
Call Trace:
 [<c104f912>] ? warn_slowpath_common+0x72/0xa0
 [<c113d620>] ? iput_final+0x1d0/0x1e0
 [<c113d620>] ? iput_final+0x1d0/0x1e0
 [<c104f962>] ? warn_slowpath_null+0x22/0x30
 [<c113d620>] ? iput_final+0x1d0/0x1e0
 [<c113d65d>] ? iput+0x2d/0x40
 [<e09b64ba>] ? sf_read_super_26+0x3ba/0x680 [vboxsf]
 [<c1129617>] ? mount_nodev+0x47/0xa0
 [<e09b6100>] ? sf_read_super_26+0x0/0x680 [vboxsf]
 [<c112968f>] ? get_sb_nodev+0x1f/0x40
 [<e09b6100>] ? sf_read_super_26+0x0/0x680 [vboxsf]
 [<e09b6031>] ? sf_get_sb+0x21/0x30 [vboxsf]
 [<e09b6100>] ? sf_read_super_26+0x0/0x680 [vboxsf]
 [<c1129264>] ? vfs_kern_mount+0x184/0x230
 [<c113f893>] ? get_fs_type+0x33/0xb0
 [<c112936e>] ? do_kern_mount+0x3e/0xe0
 [<c11427c3>] ? do_mount+0x1b3/0x1e0
 [<c1142b5b>] ? sys_mount+0x6b/0xa0
 [<c1509904>] ? syscall_call+0x7/0xb
---[ end trace 4e53f1795e2a3127 ]---