Hello,

in 4.8.11 and 4.9-rc7, I get an Oops (see below), when I try to activate
and afterward deactivate a second gadget configfs configuration, like this:

mkdir /sys/kernel/config/usb_gadget/acm
cd /sys/kernel/config/usb_gadget/acm
echo 0x0200 > bcdUSB
echo 0x0525 > idVendor
echo 0xa4a7 > idProduct
echo 0x03 > bDeviceClass
mkdir functions/acm.1
mkdir configs/c.2
ln -s functions/acm.1/ configs/c.2
echo dummy_udc.0 > UDC

mkdir /sys/kernel/config/usb_gadget/gser
cd /sys/kernel/config/usb_gadget/gser
echo 0x0525 > idVendor
echo 0xa4a6 > idProduct
echo 0xff > bDeviceClass
mkdir functions/gser.1
mkdir configs/c.1
ln -s functions/gser.1/ configs/c.1
echo dummy_udc.0 > UDC

echo > UDC


I had expected that writing "dummy_udc.0" to
/sys/kernel/config/usb_gadget/gser/UDC would fail, because the UDC is
already bound to another gadget configuration
(/sys/kernel/config/usb_gadget/acm/UDC). However, this doesn't give me
an error, but the ACM configuration remains active.

The same happens when using a real UDC (PLX3380 via driver net2280 in my
case) instead of dummy_hcd.



[  600.276226] <BUG: unable to handle kernel NULL pointer dereference
at           (null)
[  600.276841] IP: [<ffffffff94f5e5e9>] __list_del_entry+0x29/0xc0
[  600.277450] PGD 41b4c5067
[  600.277455] PUD 41a598067
[  600.278063] PMD 0

[  600.278680] Oops: 0000 [#1] SMP
[  600.279297] Modules linked in: cdc_acm usb_f_fs usb_f_serial
usb_f_acm u_serial libcomposite configfs dummy_hcd bnep intel_rapl
x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm
snd_hda_codec_hdmi irqbypass crct10dif_pclmul crc32_pclmul
ghash_clmulni_intel aesni_intel aes_x86_64 lrw gf128mul glue_helper
ablk_helper cryptd snd_hda_codec_realtek snd_hda_codec_generic serio_raw
uvcvideo videobuf2_vmalloc btusb snd_usb_audio snd_hda_intel
videobuf2_memops btrtl snd_hda_codec snd_hda_core snd_usbmidi_lib btbcm
videobuf2_v4l2 btintel snd_hwdep videobuf2_core snd_seq_midi bluetooth
snd_seq_midi_event videodev xpad efi_pstore snd_pcm_oss rfkill joydev
media crc16 ff_memless snd_mixer_oss snd_rawmidi nls_ascii snd_pcm
snd_seq snd_seq_device nls_cp437 mei_me snd_timer vfat sg udc_core
lpc_ich fat
[  600.280153]  efivars mfd_core mei snd soundcore battery nuvoton_cir
rc_core evdev intel_smartconnect ie31200_edac edac_core shpchp tpm_tis
tpm_tis_core tpm parport_pc ppdev lp parport efivarfs autofs4 btrfs xor
raid6_pq hid_logitech_hidpp hid_logitech_dj hid_generic usbhid hid uas
usb_storage sr_mod cdrom sd_mod ahci libahci nouveau i915 crc32c_intel
i2c_algo_bit psmouse ttm xhci_pci libata scsi_mod ehci_pci
drm_kms_helper xhci_hcd ehci_hcd r8169 mii usbcore drm nvme nvme_core
fjes button [last unloaded: net2280]
[  600.281688] CPU: 5 PID: 829 Comm: bash Not tainted 4.9.0-rc7 #1
[  600.282424] Hardware name: To Be Filled By O.E.M. To Be Filled By
O.E.M./Z77 Extreme3, BIOS P1.50 07/11/2013
[  600.283163] task: ffff880419ce4040 task.stack: ffffc90002ed4000
[  600.283910] RIP: 0010:[<ffffffff94f5e5e9>]  [<ffffffff94f5e5e9>]
__list_del_entry+0x29/0xc0
[  600.284668] RSP: 0018:ffffc90002ed7d68  EFLAGS: 00010207
[  600.285426] RAX: 0000000000000000 RBX: ffff88041787ec30 RCX:
dead000000000200
[  600.286192] RDX: 0000000000000000 RSI: ffff880417482002 RDI:
ffff88041787ec30
[  600.286955] RBP: ffffc90002ed7d68 R08: 0000000000000000 R09:
0000000000000010
[  600.287728] R10: 0000000000000000 R11: ffff880419ce4040 R12:
ffff88041787eb68
[  600.288513] R13: ffff88041787eaa8 R14: ffff88041560a2c0 R15:
0000000000000001
[  600.289300] FS:  00007fe4e49b8700(0000) GS:ffff88042f340000(0000)
knlGS:0000000000000000
[  600.290097] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  600.290893] CR2: 0000000000000000 CR3: 000000041b4c4000 CR4:
00000000001406e0
[  600.291696] Stack:
[  600.292504]  ffffc90002ed7d80 ffffffff94f5e68d ffffffffc0ae5ef0
ffffc90002ed7da0
[  600.293327]  ffffffffc0ae22aa ffff88041787e800 ffff88041787e800
ffffc90002ed7dc0
[  600.294153]  ffffffffc0d7a727 ffffffff952273fa ffff88041aba5760
ffffc90002ed7df8
[  600.294985] Call Trace:
[  600.295809]  [<ffffffff94f5e68d>] list_del+0xd/0x30
[  600.296653]  [<ffffffffc0ae22aa>]
usb_gadget_unregister_driver+0xaa/0xc0 [udc_core]
[  600.297496]  [<ffffffffc0d7a727>] unregister_gadget+0x27/0x60
[libcomposite]
[  600.298342]  [<ffffffff952273fa>] ? mutex_lock+0x1a/0x30
[  600.299188]  [<ffffffffc0d7a9b8>] gadget_dev_desc_UDC_store+0x88/0xe0
[libcomposite]
[  600.300046]  [<ffffffffc0af8aa0>] configfs_write_file+0xa0/0x100
[configfs]
[  600.300904]  [<ffffffff94e10d27>] __vfs_write+0x37/0x160
[  600.301761]  [<ffffffff94e31430>] ? __fd_install+0x30/0xd0
[  600.302627]  [<ffffffff95229dae>] ? _raw_spin_unlock+0xe/0x10
[  600.303494]  [<ffffffff94e11458>] vfs_write+0xb8/0x1b0
[  600.304364]  [<ffffffff94e128f8>] SyS_write+0x58/0xc0
[  600.305228]  [<ffffffff94e31594>] ? __close_fd+0x94/0xc0
[  600.306103]  [<ffffffff9522a0fb>] entry_SYSCALL_64_fastpath+0x1e/0xad
[  600.306980] Code: 66 90 55 48 8b 07 48 b9 00 01 00 00 00 00 ad de 48
8b 57 08 48 89 e5 48 39 c8 74 29 48 b9 00 02 00 00 00 00 ad de 48 39 ca
74 3a <4c> 8b 02 4c 39 c7 75 52 4c 8b 40 08 4c 39 c7 75 66 48 89 50 08
[  600.308031] RIP  [<ffffffff94f5e5e9>] __list_del_entry+0x29/0xc0
[  600.308960]  RSP <ffffc90002ed7d68>
[  600.309880] CR2: 0000000000000000
[  600.310845] ---[ end trace 99fc090ab3ff6cbc ]---
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