ウォッチドッグタイマーと vxfs により、"INFO: task khugepaged:pppp blocked for more than xxx seconds" というメッセージがログに記録され、RHEL 6 で IO がハングする

Issue

• タスクが xxx 秒以上ハングしていることを示す以下のようなメッセージがログに記録されます。デフォルトの時間は 120 秒です。

INFO: task khugepaged:421 blocked for more than 120 seconds. 
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 
khugepaged    D 0000000000000020     0   421      2 0x00000000 
 ffff8820100e3c90 0000000000000046 0000000000000000 ffff88000002dd40 
 ffff8820100e1540 00000000004352da ffff8820100e3d40 ffffffff8112bae3 
 ffff8820100e1af8 ffff8820100e3fd8 000000000000fb88 ffff8820100e1af8 
Call Trace: 
 [<ffffffff8112bae3>] ? __alloc_pages_nodemask+0x113/0x8d0 
 [<ffffffff8150fc45>] rwsem_down_failed_common+0x95/0x1d0 
 [<ffffffff8150fda3>] rwsem_down_write_failed+0x23/0x30 
 [<ffffffff812833e3>] call_rwsem_down_write_failed+0x13/0x20 
 [<ffffffff8150f2a2>] ? down_write+0x32/0x40 
 [<ffffffff81179eb6>] khugepaged+0x7f6/0x1310 
 [<ffffffff81096c80>] ? autoremove_wake_function+0x0/0x40 
 [<ffffffff811796c0>] ? khugepaged+0x0/0x1310 
 [<ffffffff81096916>] kthread+0x96/0xa0 
 [<ffffffff8100c0ca>] child_rip+0xa/0x20 
 [<ffffffff81096880>] ? kthread+0x0/0xa0 
 [<ffffffff8100c0c0>] ? child_rip+0x0/0x20 
<snip>
INFO: task vx_naio_worker:41196 blocked for more than 120 seconds. 
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 
vx_naio_worke D 0000000000000000     0 41196      2 0x00000080 
 ffff8809e9ee3c40 0000000000000046 ffff880099b56798 ffff880099b56768 
 ffff880123a95578 000000000022feba ffff880123a95540 0000000000000000 
 ffff88080815f098 ffff8809e9ee3fd8 000000000000fb88 ffff88080815f098 
Call Trace: 
 [<ffffffffa05610ce>] vx_svar_sleep_unlock+0x6e/0xd0 [vxfs] 
 [<ffffffffa0560e60>] ? vx_wq_wakeup_function+0x0/0x20 [vxfs] 
 [<ffffffff8106317e>] ? try_to_wake_up+0x24e/0x3e0 
 [<ffffffffa0537b09>] vx_rwsleep_rec_lock+0xd9/0x110 [vxfs] 
 [<ffffffffa05044b2>] vx_recsmp_lock+0x12/0x20 [vxfs] 
 [<ffffffffa0620f75>] vx_write_common+0x1e5/0x860 [vxfs] 
 [<ffffffff81051419>] ? __wake_up_common+0x59/0x90 
 [<ffffffffa059f110>] vx_vop_write+0x20/0x30 [vxfs] 
 [<ffffffffa057f2e2>] vx_naio_do_work+0x1a2/0x440 [vxfs] 
 [<ffffffffa057f609>] vx_naio_worker+0x89/0x2b0 [vxfs] 
 [<ffffffffa057f580>] ? vx_naio_worker+0x0/0x2b0 [vxfs] 
 [<ffffffffa059388b>] vx_kthread_init+0x7b/0x90 [vxfs] 
 [<ffffffffa057f580>] ? vx_naio_worker+0x0/0x2b0 [vxfs] 
 [<ffffffff8100c0ca>] child_rip+0xa/0x20 
 [<ffffffffa057f580>] ? vx_naio_worker+0x0/0x2b0 [vxfs] 
 [<ffffffffa0593810>] ? vx_kthread_init+0x0/0x90 [vxfs] 
 [<ffffffff8100c0c0>] ? child_rip+0x0/0x20