Suse11sp4 operating system crash when backup oracle11g database using BLB option

crashdump log:

<6>[5258663.115395] EXT3-fs (dm-22): mounted filesystem with ordered data mode
<6>[5431207.839871] 31828: cvbf_attach_block_device(): Attaching to 253:20
<3>[5431207.839877] 31828: ERROR: cvbf_attach_block_device(): Device 253:20 is already attached
<6>[5431241.625666] kjournald starting.  Commit interval 15 seconds
<6>[5431241.626067] EXT3-fs (dm-22): mounted filesystem with ordered data mode
<3>[5435880.559354] INFO: task CvMountd:11008 blocked for more than 180 seconds.
<3>[5435880.559362] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
<6>[5435880.559370] CvMountd        D ffff88084d8a3c24     0 11008      1 0x00000000
<4>[5435880.559381]  ffff880180d1fd38 0000000000000086 ffff880180d1e010 0000000000013400
<4>[5435880.559394]  0000000000013400 0000000000013400 0000000000013400 ffff880180d1ffd8
<4>[5435880.559405]  ffff880180d1ffd8 0000000000013400 ffff880266776240 ffff88084fc40480
<4>[5435880.559416] Call Trace:
<4>[5435880.559460]  [<ffffffffa0326c16>] start_this_handle+0x2f6/0x3a0 [jbd]
<4>[5435880.559485]  [<ffffffffa0326e9e>] journal_start+0x9e/0xe0 [jbd]
<4>[5435880.559505]  [<ffffffffa0350aa7>] ext3_unlink+0x57/0x230 [ext3]
<4>[5435880.559534]  [<ffffffff81170e52>] vfs_unlink+0xb2/0x120
<4>[5435880.559546]  [<ffffffff81173fe1>] do_unlinkat+0x231/0x240
<4>[5435880.559565]  [<ffffffff8147c3be>] system_call_fastpath+0x22/0x27
<4>[5435880.559592]  [<00007fd76d9216b7>] 0x7fd76d9216b6
<0>[5435880.559598] Kernel panic - not syncing: hung_task: blocked tasks
<4>[5435880.559612] Pid: 172, comm: khungtaskd Tainted: P           EN  3.0.101-108.57-default #1

question:

cvbf_attach_block_device(): Device 253:20 is already attached

why does CvMountd to always attached this device?