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    Subjectdebugging oops after disconnecting Nexio USB touchscreen
    Date
    Hello,
    I have problems debbugging an oops. It happens when Nexio USB touchscreen
    (using my new code http://lkml.org/lkml/2009/11/25/568) is disconnected:

    BUG: unable to handle kernel NULL pointer dereference at 00000048
    IP: [<f7c38afd>] start_unlink_async+0xb2/0x160 [ehci_hcd]
    *pde = 00000000
    Oops: 0000 [#1] SMP
    last sysfs file: /sys/devices/pci0000:00/0000:00:1b.0/sound/card0/controlC0/uevent
    Modules linked in: uvesafb cn i915 drm i2c_algo_bit joydev usbtouchscreen loop snd_usb_audio snd_usb_lib snd_rawmidi snd_seq_device
    snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_timer snd ftdi_sio soundcore snd_page_alloc
    gspca_ov519 usblp usbhid hid usbserial gspca_main videodev rng_core v4l1_compat i2c_i801 i2c_core processor pcspkr psmouse
    asus_atk0110 evdev serio_raw button ext3 jbd mbcache usb_storage sd_mod crc_t10dif ata_generic ata_piix libata scsi_mod
    ide_pci_generic r8169 mii video output uhci_hcd intel_agp agpgart ehci_hcd ide_core usbcore nls_base thermal fan thermal_sys
    Pid: 195, comm: khubd Not tainted (2.6.31 #1) B202
    EIP: 0060:[<f7c38afd>] EFLAGS: 00010003 CPU: 0
    EIP is at start_unlink_async+0xb2/0x160 [ehci_hcd]
    EAX: 00000000 EBX: f648c8e8 ECX: 78bd7dee EDX: 78bd7dee
    ESI: 00000000 EDI: f65fc080 EBP: 00010030 ESP: f65bfddc
    DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
    Process hbuhd (pid: 195, ti=f65be000 task=f644e1c0 task.ti=f65be000)
    Stack:
    78bd7dee fffffffe f65fc080 f648c800 f648c8e8 f7c3ab29 f648c8f8 00000246
    <0> 00000000 78bd7dee f7c3e278 f648c800 f605d840 fffffffe f7c977fc f6481800
    <0> 78bd7dee 00000000 f605d840 00000246 fffffffe f7c9795d 78bd7dee f605d840
    Call Trace:
    [<f7c3ab29>] ? ehci_urb_dequeue+0x7c/0x11a [ehci_hcd]
    [<f7c977fc>] ? unlink1+0xaa/0xc7 [usbcore]
    [<f7c9795d>] ? usb_hcd_unlink_urb+0x57/0x84 [usbcore]
    [<f7c98b28>] ? usb_kill_urb+0x40/0xbe [usbcore]
    [<c1034ec2>] ? default_wake_function+0x0/0x2b
    [<f7c99ff9>] ? usb_start_wait_urb+0x6e/0xb0 [usbcore]
    [<f7c9a2cf>] ? usb_control_msg+0x10a/0x136 [usbcore]
    [<f7c92e46>] ? hub_port_status+0x77/0xf7 [usbcore]
    [<f7c95f9d>] ? hub_thread+0x56d/0xe14 [usbcore]
    [<c1050003>] ? autoremove_wake_function+0x0/0x4f
    [<f7c95a30>] ? hub_thread+0x0/0xe14 [usbcore]
    [<c104fc73>] ? kthread+0x7a/0x7f
    [<c104fbf9>] ? kthread+0x0/0x7f
    [<c1004027>] ? kernel_thread_helper+0x7/0x10
    Code: 00 fb e9 bb 00 00 00 c6 46 68 02 89 f0 e8 ee e8 ff ff 85 db 89 c7 89 43 18 75 06 68 c5 e4 c3 f7 e8 b4 5f 68 c9 50 8b 43 14 89 c6
    <8b> 40 48 39 f8 75 f7 85 f6 75 0b 68 0c e5 c3 f7 e8 99 5f 68 c9
    EIP: [<f7c38afd>] start_unlink_async+0xb2/0x160 [ehci_hcd] SS:ESP 0068:f65bfddc
    CR2: 0000000000000048
    ---[ end trace 040b72a526aa0755 ]---


    It does not happen everytime - sometimes it survives the first disconnect.
    Tried adding printk()s to start_unlink_async function - and the oops does not appear.
    Looks like a race. It might be a bug in my code but I'm not able to find it.

    It also happens only when the touchscreen is connected through a hub:
    Bus 001 Device 002: ID 2001:f103 D-Link Corp. [hex] DUB-H7 7-port USB 2.0 hub
    When connected directly to the machine, it does not oops.

    Tried decodecode:
    Code: 00 fb e9 bb 00 00 00 c6 46 68 02 89 f0 e8 ee e8 ff ff 85 db 89 c7 89 43 18 75 06 68 c5 e4 c3 f7 e8 b4 5f 68 c9 50 8b 43 14 89 c6 <8b> 40 48 39 f8 75
    f7 85 f6 75 0b 68 0c e5 c3 f7 e8 99 5f 68 c9
    All code
    ========
    0: 00 fb add %bh,%bl
    2: e9 bb 00 00 00 jmp 0xc2
    7: c6 46 68 02 movb $0x2,0x68(%esi)
    b: 89 f0 mov %esi,%eax
    d: e8 ee e8 ff ff call 0xffffe900
    12: 85 db test %ebx,%ebx
    14: 89 c7 mov %eax,%edi
    16: 89 43 18 mov %eax,0x18(%ebx)
    19: 75 06 jne 0x21
    1b: 68 c5 e4 c3 f7 push $0xf7c3e4c5
    20: e8 b4 5f 68 c9 call 0xc9685fd9
    25: 50 push %eax
    26: 8b 43 14 mov 0x14(%ebx),%eax
    29: 89 c6 mov %eax,%esi
    2b:* 8b 40 48 mov 0x48(%eax),%eax <-- trapping instruction
    2e: 39 f8 cmp %edi,%eax
    30: 75 f7 jne 0x29
    32: 85 f6 test %esi,%esi
    34: 75 0b jne 0x41
    36: 68 0c e5 c3 f7 push $0xf7c3e50c
    3b: e8 99 5f 68 c9 call 0xc9685fd9

    Code starting with the faulting instruction
    ===========================================
    0: 8b 40 48 mov 0x48(%eax),%eax
    3: 39 f8 cmp %edi,%eax
    5: 75 f7 jne 0xfffffffe
    7: 85 f6 test %esi,%esi
    9: 75 0b jne 0x16
    b: 68 0c e5 c3 f7 push $0xf7c3e50c
    10: e8 99 5f 68 c9 call 0xc9685fae

    and "make drivers/usb/host/ehci-hcd.s" but I'm not able to find the above code in ehci-hcd.s.

    What am I doing wrong?

    --
    Ondrej Zary


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