A new regression was introduced between -rc3 and -rc4:

The USB mouse I use with my laptop is causing a BUG when inserted.  It works at that
point, but if removed and re-inserted, it is ignored.  Also, after the 2nd insert,
other USB devices (like my thumb drive) are also ignored.

[   37.450777] BUG: unable to handle kernel NULL pointer dereference at (null)
[   37.451148] IP: [<ffffffff817d0991>] hiddev_open+0xc1/0x220
[   37.452036] PGD 1131a0067 PUD 113036067 PMD 0 
[   37.452924] Oops: 0000 [#1] PREEMPT SMP 
[   37.453336] last sysfs file: /sys/devices/platform/toshiba_acpi/backlight/toshiba/max_brightness
[   37.453336] CPU 1 
[   37.453336] Modules linked in: tpm_infineon iwlagn iwlcore tifm_7xx1 tpm_tis toshiba_bluetooth toshiba_acpi tifm_core pcmcia sdhci_pci yenta_socket sdhci [last unloaded: scsi_wait_scan]
[   37.453336] 
[   37.453336] Pid: 3117, comm: hald-probe-hidd Not tainted 2.6.36-rc4-00166-g151b6a5 #28 Portable PC/TECRA A9
[   37.453336] RIP: 0010:[<ffffffff817d0991>]  [<ffffffff817d0991>] hiddev_open+0xc1/0x220
[   37.453336] RSP: 0018:ffff8801130e7c28  EFLAGS: 00010286
[   37.453336] RAX: 00000000ffffffed RBX: ffff8801121a0000 RCX: 0000000000000000
[   37.453336] RDX: 0000000000000000 RSI: ffffffff81cfbfaa RDI: ffff8801121ac030
[   37.453336] RBP: ffff8801130e7c58 R08: 0000000000000010 R09: 0000000000000000
[   37.453336] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801131c10c0
[   37.453336] R13: 0000000000000000 R14: 00000000ffffffed R15: ffff88013820ac68
[   37.453336] FS:  00007f3987315700(0000) GS:ffff880002500000(0000) knlGS:0000000000000000
[   37.453336] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   37.453336] CR2: 0000000000000000 CR3: 0000000112188000 CR4: 00000000000006e0
[   37.453336] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   37.453336] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[   37.453336] Process hald-probe-hidd (pid: 3117, threadinfo ffff8801130e6000, task ffff8801399186b0)
[   37.453336] Stack:
[   37.453336]  ffff8801130e6000 00000000000000b4 ffff8801131c10c0 ffffffff81b57c20
[   37.453336] <0> ffffffff81b66420 00000000ffffffed ffff8801130e7c98 ffffffff8171794b
[   37.453336] <0> 000000000029d5f6 ffff88013b345d00 ffff88013820ac68 ffff8801131c10c0
[   37.453336] Call Trace:
[   37.453336]  [<ffffffff8171794b>] usb_open+0x10b/0x2b0
[   37.453336]  [<ffffffff81156ae0>] ? chrdev_open+0x0/0x280
[   37.453336]  [<ffffffff81156c07>] chrdev_open+0x127/0x280
[   37.453336]  [<ffffffff81156ae0>] ? chrdev_open+0x0/0x280
[   37.453336]  [<ffffffff81151508>] __dentry_open+0x108/0x3a0
[   37.453336]  [<ffffffff811518b4>] nameidata_to_filp+0x54/0x70
[   37.453336]  [<ffffffff8115f668>] do_last+0x3b8/0x6c0
[   37.453336]  [<ffffffff811618a8>] do_filp_open+0x228/0x670
[   37.453336]  [<ffffffff81919ac5>] ? T.827+0x135/0x230
[   37.453336]  [<ffffffff8116c4aa>] ? alloc_fd+0xfa/0x140
[   37.453336]  [<ffffffff811512c5>] do_sys_open+0x65/0x130
[   37.453336]  [<ffffffff811513d0>] sys_open+0x20/0x30
[   37.453336]  [<ffffffff81037c1b>] system_call_fastpath+0x16/0x1b
[   37.453336] Code: 30 c0 00 00 48 c7 c6 aa bf cf 81 e8 9a 7d 8d ff 4c 89 ab 18 c0 00 00 b8 ed ff ff ff 49 89 9c 24 98 00 00 00 48 8b 93 18 c0 00 00 <44> 8b 02 45 85 c0 0f 84 a8 00 00 00 8b 42 04 8d 48 01 85 c0 89 
[   37.453336] RIP  [<ffffffff817d0991>] hiddev_open+0xc1/0x220
[   37.453336]  RSP <ffff8801130e7c28>
[   37.453336] CR2: 0000000000000000
[   37.495310] ---[ end trace a76b3a74914412d8 ]---

I bisected this phenomenon to:

8fe294caf8c868edd9046251824a0af91991bf43 is the first bad commit
commit 8fe294caf8c868edd9046251824a0af91991bf43
Author: Guillaume Chazarain <guichaz@gmail.com>
Date:   Sun Sep 12 21:32:35 2010 +0200

    HID: fix hiddev's use of usb_find_interface
    
    My macbook infrared remote control was broken by commit
    bd25f4dd6972755579d0ea50d1a5ace2e9b00d1a ("HID: hiddev: use
    usb_find_interface, get rid of BKL").
    
    This device appears in dmesg as:
    apple 0003:05AC:8242.0001: hiddev0,hidraw0: USB HID v1.11 Device
    [Apple Computer, Inc. IR Receiver] on usb-0000:00:1d.2-1/input0
    
    It stopped working as lircd was getting ENODEV when opening /dev/usb/hiddev0.
    
    AFAICS hiddev_driver is a dummy driver so usb_find_interface(&hiddev_driver)
    does not find anything.
    
    The device is associated with the usbhid driver, so let's do
    usb_find_interface(&hid_driver) instead.
    
    $ ls -l /sys/devices/pci0000:00/0000:00:1d.2/usb7/7-1/7-1:1.0/usb/hiddev0/device/driver
    lrwxrwxrwx 1 root root 0 2010-09-12 16:28 /sys/devices/pci0000:00/0000:00:1d.2/usb7/7-1/7-1:1.0/usb/hiddev0/device/driver -> ../../../../../../bus/usb/drivers/usbhid
    
    Signed-off-by: Guillaume Chazarain <guichaz@gmail.com>
    Signed-off-by: Jiri Kosina <jkosina@suse.cz>

:040000 040000 a7db28b9b84792aa51a1027daebb627150892837 84209dde8d0d2ef3c1d58a20586060947890fc80 M      drivers

lsusb also gets stuck like so:

# cat /proc/4306/stack 
[<ffffffff81719e3c>] usbdev_open+0x11c/0x2e0
[<ffffffff81156c07>] chrdev_open+0x127/0x280
[<ffffffff81151508>] __dentry_open+0x108/0x3a0
[<ffffffff811518b4>] nameidata_to_filp+0x54/0x70
[<ffffffff8115f668>] do_last+0x3b8/0x6c0
[<ffffffff811618a8>] do_filp_open+0x228/0x670
[<ffffffff811512c5>] do_sys_open+0x65/0x130
[<ffffffff811513d0>] sys_open+0x20/0x30
[<ffffffff81037c1b>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

The commit 8fe294c reverts cleanly from 2.6.36-rc4-00166-g151b6a5, and solves this
problem.

Config, dmesg, and lsusb (after revert) are attached.

The system is Gentoo unstable 64bit, w/ hal-0.5.14-r2 and udev-161.

I'm happy to test patches in lieu of a revert, since it was a fix to a
different regression.