USB: serial: fix race between probe and open

commit a65a6f14dc24a90bde3f5d0073ba2364476200bf upstream.

Fix race between probe and open by making sure that the disconnected
flag is not cleared until all ports have been registered.

A call to tty_open while probe is running may get a reference to the
serial structure in serial_install before its ports have been
registered. This may lead to usb_serial_core calling driver open before
port is fully initialised.

With ftdi_sio this result in the following NULL-pointer dereference as
the private data has not been initialised at open:

[  199.698286] IP: [<f811a089>] ftdi_open+0x59/0xe0 [ftdi_sio]
[  199.698297] *pde = 00000000
[  199.698303] Oops: 0000 [#1] PREEMPT SMP
[  199.698313] Modules linked in: ftdi_sio usbserial
[  199.698323]
[  199.698327] Pid: 1146, comm: ftdi_open Not tainted 3.2.11 #70 Dell Inc. Vostro 1520/0T816J
[  199.698339] EIP: 0060:[<f811a089>] EFLAGS: 00010286 CPU: 0
[  199.698344] EIP is at ftdi_open+0x59/0xe0 [ftdi_sio]
[  199.698348] EAX: 0000003e EBX: f5067000 ECX: 00000000 EDX: 80000600
[  199.698352] ESI: f48d8800 EDI: 00000001 EBP: f515dd54 ESP: f515dcfc
[  199.698356]  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
[  199.698361] Process ftdi_open (pid: 1146, ti=f515c000 task=f481e040 task.ti=f515c000)
[  199.698364] Stack:
[  199.698368]  f811a9fe f811a9e0 f811b3ef 00000000 00000000 00001388 00000000 f4a86800
[  199.698387]  00000002 00000000 f806e68e 00000000 f532765c f481e040 00000246 22222222
[  199.698479]  22222222 22222222 22222222 f5067004 f5327600 f5327638 f515dd74 f806e6ab
[  199.698496] Call Trace:
[  199.698504]  [<f806e68e>] ? serial_activate+0x2e/0x70 [usbserial]
[  199.698511]  [<f806e6ab>] serial_activate+0x4b/0x70 [usbserial]
[  199.698521]  [<c126380c>] tty_port_open+0x7c/0xd0
[  199.698527]  [<f806e660>] ? serial_set_termios+0xa0/0xa0 [usbserial]
[  199.698534]  [<f806e76f>] serial_open+0x2f/0x70 [usbserial]
[  199.698540]  [<c125d07c>] tty_open+0x20c/0x510
[  199.698546]  [<c10e9eb7>] chrdev_open+0xe7/0x230
[  199.698553]  [<c10e48f2>] __dentry_open+0x1f2/0x390
[  199.698559]  [<c144bfec>] ? _raw_spin_unlock+0x2c/0x50
[  199.698565]  [<c10e4b76>] nameidata_to_filp+0x66/0x80
[  199.698570]  [<c10e9dd0>] ? cdev_put+0x20/0x20
[  199.698576]  [<c10f3e08>] do_last+0x198/0x730
[  199.698581]  [<c10f4440>] path_openat+0xa0/0x350
[  199.698587]  [<c10f47d5>] do_filp_open+0x35/0x80
[  199.698593]  [<c144bfec>] ? _raw_spin_unlock+0x2c/0x50
[  199.698599]  [<c10ff110>] ? alloc_fd+0xc0/0x100
[  199.698605]  [<c10f0b72>] ? getname_flags+0x72/0x120
[  199.698611]  [<c10e4450>] do_sys_open+0xf0/0x1c0
[  199.698617]  [<c11fcc08>] ? trace_hardirqs_on_thunk+0xc/0x10
[  199.698623]  [<c10e458e>] sys_open+0x2e/0x40
[  199.698628]  [<c144c990>] sysenter_do_call+0x12/0x36
[  199.698632] Code: 85 89 00 00 00 8b 16 8b 4d c0 c1 e2 08 c7 44 24 14 88 13 00 00 81 ca 00 00 00 80 c7 44 24 10 00 00 00 00 c7 44 24 0c 00 00 00 00 <0f> b7 41 78 31 c9 89 44 24 08 c7 44 24 04 00 00 00 00 c7 04 24
[  199.698884] EIP: [<f811a089>] ftdi_open+0x59/0xe0 [ftdi_sio] SS:ESP 0068:f515dcfc
[  199.698893] CR2: 0000000000000078
[  199.698925] ---[ end trace 77c43ec023940cff ]---

Reported-and-tested-by: Ken Huang <csuhgw@gmail.com>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>