After installing fresh Kubuntu 11.04 Natty on my desktop PC, I experienced some issues with application and process hangs. There is also a problem with my USB 3 hard disk. These sort of problems did not happen on Kubuntu 10.10 installed on the same PC (on separate partition).

The hangs manifest themselves with kernel log messages like these:

[  960.480151] INFO: task amarok:2505 blocked for more than 120 seconds.
[  960.480153] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  960.480155] amarok          D 0000000000000000     0  2505      1 0x00000000
[  960.480158]  ffff8800a556bb38 0000000000000086 ffff8800a556bfd8 ffff8800a556a000
[  960.480162]  0000000000013d00 ffff8800cb7f3178 ffff8800a556bfd8 0000000000013d00
[  960.480165]  ffffffff81a0b020 ffff8800cb7f2dc0 ffffea000242ac58 ffff88012704c870
[  960.480169] Call Trace:
[  960.480172]  [<ffffffff815c19f7>] __mutex_lock_slowpath+0xf7/0x180
[  960.480175]  [<ffffffff815c144b>] mutex_lock+0x2b/0x50
[  960.480180]  [<ffffffffa0d0ad42>] video_open+0x102/0x400 [cx8800]
[  960.480183]  [<ffffffff815c2cbe>] ? _raw_spin_lock+0xe/0x20
[  960.480186]  [<ffffffff8117c55d>] ? __d_lookup+0x10d/0x170
[  960.480191]  [<ffffffffa0ca0731>] v4l2_open+0x101/0x130 [videodev]
[  960.480194]  [<ffffffff81168f4a>] chrdev_open+0xda/0x1f0
[  960.480197]  [<ffffffff81168e70>] ? chrdev_open+0x0/0x1f0
[  960.480200]  [<ffffffff81162cee>] __dentry_open+0xce/0x2f0
[  960.480202]  [<ffffffff8116ef33>] ? generic_permission+0x23/0xc0
[  960.480205]  [<ffffffff811641e1>] nameidata_to_filp+0x71/0x80
[  960.480208]  [<ffffffff811733c8>] finish_open+0xc8/0x1b0
[  960.480210]  [<ffffffff811725b7>] ? do_path_lookup+0x87/0x160
[  960.480213]  [<ffffffff81173b88>] do_filp_open+0x2c8/0x7c0
[  960.480216]  [<ffffffff81172902>] ? user_path_at+0x62/0xa0
[  960.480219]  [<ffffffff81131d4d>] ? handle_mm_fault+0x16d/0x250
[  960.480222]  [<ffffffff812e6c47>] ? __strncpy_from_user+0x27/0x60
[  960.480225]  [<ffffffff81180ea7>] ? alloc_fd+0xf7/0x150
[  960.480228]  [<ffffffff8116425a>] do_sys_open+0x6a/0x150
[  960.480230]  [<ffffffff81164360>] sys_open+0x20/0x30
[  960.480233]  [<ffffffff8100c002>] system_call_fastpath+0x16/0x1b
[ 1080.480027] INFO: task knotify4:1663 blocked for more than 120 seconds.
[ 1080.480030] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1080.480032] knotify4        D 0000000000000000     0  1663      1 0x00000000
[ 1080.480036]  ffff880123a2bb28 0000000000000082 ffff880123a2bfd8 ffff880123a2a000
[ 1080.480040]  0000000000013d00 ffff880121003178 ffff880123a2bfd8 0000000000013d00
[ 1080.480044]  ffff8800cb7e16e0 ffff880121002dc0 ffffffff81060a27 ffff88012704c870
[ 1080.480048] Call Trace:
[ 1080.480054]  [<ffffffff81060a27>] ? mutex_spin_on_owner+0x97/0xd0
[ 1080.480059]  [<ffffffff815c19f7>] __mutex_lock_slowpath+0xf7/0x180
[ 1080.480069]  [<ffffffff812e4f61>] ? vsnprintf+0x221/0x620
[ 1080.480072]  [<ffffffff815c144b>] mutex_lock+0x2b/0x50
[ 1080.480076]  [<ffffffffa0b2d10f>] cx8802_request_acquire+0x5f/0xf0 [cx8802]
[ 1080.480081]  [<ffffffffa0e87e08>] mpeg_open+0x78/0x270 [cx88_blackbird]
[ 1080.480084]  [<ffffffff8117c55d>] ? __d_lookup+0x10d/0x170
[ 1080.480092]  [<ffffffffa0ca0731>] v4l2_open+0x101/0x130 [videodev]
[ 1080.480096]  [<ffffffff81168f4a>] chrdev_open+0xda/0x1f0
[ 1080.480099]  [<ffffffff81168e70>] ? chrdev_open+0x0/0x1f0
[ 1080.480102]  [<ffffffff81162cee>] __dentry_open+0xce/0x2f0
[ 1080.480105]  [<ffffffff8116ef33>] ? generic_permission+0x23/0xc0
[ 1080.480108]  [<ffffffff811641e1>] nameidata_to_filp+0x71/0x80
[ 1080.480111]  [<ffffffff811733c8>] finish_open+0xc8/0x1b0
[ 1080.480113]  [<ffffffff811725b7>] ? do_path_lookup+0x87/0x160
[ 1080.480116]  [<ffffffff81173b88>] do_filp_open+0x2c8/0x7c0
[ 1080.480119]  [<ffffffff81172902>] ? user_path_at+0x62/0xa0
[ 1080.480122]  [<ffffffff811663f1>] ? get_empty_filp+0xa1/0x170
[ 1080.480125]  [<ffffffff812e6c47>] ? __strncpy_from_user+0x27/0x60
[ 1080.480128]  [<ffffffff81180ea7>] ? alloc_fd+0xf7/0x150
[ 1080.480131]  [<ffffffff8116425a>] do_sys_open+0x6a/0x150
[ 1080.480134]  [<ffffffff81164360>] sys_open+0x20/0x30
[ 1080.480137]  [<ffffffff8100c002>] system_call_fastpath+0x16/0x1b
[ 1080.480147] INFO: task dolphin:1842 blocked for more than 120 seconds.
[ 1080.480148] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1080.480150] dolphin         D 0000000000000000     0  1842      1 0x00000004
[ 1080.480154]  ffff8800cb4f3b38 0000000000000082 ffff8800cb4f3fd8 ffff8800cb4f2000
[ 1080.480157]  0000000000013d00 ffff8800cb7f4858 ffff8800cb4f3fd8 0000000000013d00
[ 1080.480161]  ffffffff81a0b020 ffff8800cb7f44a0 ffffea000267b0d0 ffff88012704c870
[ 1080.480164] Call Trace:
[ 1080.480168]  [<ffffffff815c19f7>] __mutex_lock_slowpath+0xf7/0x180
[ 1080.480171]  [<ffffffff815c144b>] mutex_lock+0x2b/0x50
[ 1080.480176]  [<ffffffffa0d0ad42>] video_open+0x102/0x400 [cx8800]
[ 1080.480179]  [<ffffffff815c2cbe>] ? _raw_spin_lock+0xe/0x20
[ 1080.480181]  [<ffffffff8117c55d>] ? __d_lookup+0x10d/0x170
[ 1080.480186]  [<ffffffffa0ca0731>] v4l2_open+0x101/0x130 [videodev]
[ 1080.480190]  [<ffffffff81168f4a>] chrdev_open+0xda/0x1f0
[ 1080.480192]  [<ffffffff81168e70>] ? chrdev_open+0x0/0x1f0
[ 1080.480195]  [<ffffffff81162cee>] __dentry_open+0xce/0x2f0
[ 1080.480198]  [<ffffffff8116ef33>] ? generic_permission+0x23/0xc0
[ 1080.480200]  [<ffffffff811641e1>] nameidata_to_filp+0x71/0x80
[ 1080.480203]  [<ffffffff811733c8>] finish_open+0xc8/0x1b0
[ 1080.480206]  [<ffffffff811725b7>] ? do_path_lookup+0x87/0x160
[ 1080.480208]  [<ffffffff81173b88>] do_filp_open+0x2c8/0x7c0
[ 1080.480211]  [<ffffffff81172902>] ? user_path_at+0x62/0xa0
[ 1080.480214]  [<ffffffff81131d4d>] ? handle_mm_fault+0x16d/0x250
[ 1080.480217]  [<ffffffff812e6c47>] ? __strncpy_from_user+0x27/0x60
[ 1080.480220]  [<ffffffff81180ea7>] ? alloc_fd+0xf7/0x150
[ 1080.480223]  [<ffffffff8116425a>] do_sys_open+0x6a/0x150
[ 1080.480225]  [<ffffffff81164360>] sys_open+0x20/0x30
[ 1080.480228]  [<ffffffff8100c002>] system_call_fastpath+0x16/0x1b

Attempts to kill the hung process are unsuccessful:

root@deskpc:~# ps -ef |grep amarok
myuser     2505     1  0 10:47 ?        00:00:00 /usr/bin/amarok
root      2747  2020  0 11:06 pts/3    00:00:00 grep --color=auto amarok
root@deskpc:~# kill -9 2505
root@deskpc:~# ps -ef |grep amarok
myuser     2505     1  0 10:47 ?        00:00:00 /usr/bin/amarok
root      2749  2020  0 11:06 pts/3    00:00:00 grep --color=auto amarok
root@deskpc:~# kill -9 2505
root@deskpc:~# ps -ef |grep amarok
myuser     2505     1  0 10:47 ?        00:00:00 /usr/bin/amarok
root      2751  2020  0 11:06 pts/3    00:00:00 grep --color=auto amarok
root@deskpc:~#

When trying to access my external USB3 disk, the following kernel message is observed:

[ 2169.330012] xhci_hcd 0000:06:00.0: Timeout while waiting for a slot
[ 2169.330018] hub 3-0:1.0: couldn't allocate port 1 usb_device

I am not sure the two problems (application hangs and USB3 timeouts are related) but they do not happen under Kubuntu 10.10.

Judging by the dmesg messages, it looks to me that this is a kernel (or potentially kernel driver) problem, but not sure how to debug it. Any ideas?

I ran apport-bug, but it advised me to post a question here first. Shall I report the issue on the official K/Ubuntu bugzilla?