テープデバイスの待機中にハングタスクが検出される

Issue

• システムログに、次のようなブロックされたタスクに関するメッセージが報告され、その後パニックが発生します。

INFO: task bptm:13670 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
bptm          D 0000000000000000     0 13670  13660 0x00020000
ffff88036faf3aa8 0000000000000082 0000000000000000 ffffffff8111c633
ffff8806775e6c30 ffff8804776865e0 ffff880400c02080 0000000000000020
ffff880400c02638 ffff88036faf3fd8 000000000000fb88 ffff880400c02638
Call Trace:
[<ffffffff8111c633>] ? mempool_alloc+0x63/0x140
[<ffffffff813716c0>] ? scsi_done+0x0/0x60
[<ffffffff8150e555>] schedule_timeout+0x215/0x2e0
[<ffffffff81278ee7>] ? kobject_put+0x27/0x60
[<ffffffff8135a397>] ? put_device+0x17/0x20
[<ffffffff8150e1d3>] wait_for_common+0x123/0x180
[<ffffffff81063310>] ? default_wake_function+0x0/0x20
[<ffffffff8150e2ed>] wait_for_completion+0x1d/0x20
[<ffffffffa0189f88>] st_do_scsi.clone.0+0x218/0x370 [st]
[<ffffffffa018a505>] st_int_ioctl+0x1b5/0xcf0 [st]
[<ffffffffa018cb49>] st_ioctl+0x439/0x11c0 [st]
[<ffffffff81194ed2>] vfs_ioctl+0x22/0xa0
[<ffffffff81195074>] do_vfs_ioctl+0x84/0x580
[<ffffffff8104757c>] ? __do_page_fault+0x1ec/0x480
[<ffffffff811955f1>] sys_ioctl+0x81/0xa0
[<ffffffff81086391>] ? sigprocmask+0x71/0x110
[<ffffffff811d46a0>] do_ioctl32_pointer+0x10/0x20
[<ffffffff811d6bf6>] compat_sys_ioctl+0x1a6/0x510
[<ffffffff8104e8d2>] ? sys32_rt_sigprocmask+0xd2/0x110
[<ffffffff8104d810>] sysenter_dispatch+0x7/0x2e
Kernel panic - not syncing: hung_task: blocked tasks
Pid: 257, comm: khungtaskd Not tainted 2.6.32-358.el6.x86_64 #1
Call Trace:
[<ffffffff8150cfc8>] ? panic+0xa7/0x16f
[<ffffffff810e0ab7>] ? watchdog+0x217/0x220
[<ffffffff810e08a0>] ? watchdog+0x0/0x220
[<ffffffff81096916>] ? kthread+0x96/0xa0
[<ffffffff8100c0ca>] ? child_rip+0xa/0x20
[<ffffffff81096880>] ? kthread+0x0/0xa0
[<ffffffff8100c0c0>] ? child_rip+0x0/0x20