hung tasks reported while accessing mirror device

Issue

System reports hung tasks:

INFO: task pdflush:1398 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
pdflush       D ffff81000d061ba0     0  1398    873          1399  1397 (L-TLB)
 ffff81182dd05a20 0000000000000046 0090000200000008 0000000000000001
 0000000300000000 000000000000000a ffff81182edb4080 ffff810154bf20c0
 000049b91a1eeda2 0000000000058548 ffff81182edb4268 0000000b8002e4c1
Call Trace:
 [<ffffffff8006ed98>] do_gettimeofday+0x40/0x90
 [<ffffffff800155b3>] sync_buffer+0x0/0x3f
 [<ffffffff800637de>] io_schedule+0x3f/0x67
 [<ffffffff800155ee>] sync_buffer+0x3b/0x3f
 [<ffffffff80063922>] __wait_on_bit_lock+0x36/0x66
 [<ffffffff800155b3>] sync_buffer+0x0/0x3f
 [<ffffffff800639be>] out_of_line_wait_on_bit_lock+0x6c/0x78
 [<ffffffff800a3cfd>] wake_bit_function+0x0/0x23
 [<ffffffff8003adab>] sync_dirty_buffer+0x4e/0xc3
 [<ffffffff88032c2b>] :jbd:journal_dirty_data+0x104/0x20d
 [<ffffffff8804e2b6>] :ext3:ext3_journal_dirty_data+0xf/0x34
 [<ffffffff8804d690>] :ext3:walk_page_buffers+0x65/0x8b
 [<ffffffff8804e2db>] :ext3:journal_dirty_data_fn+0x0/0xe
 [<ffffffff88050815>] :ext3:ext3_ordered_writepage+0x118/0x19c
 [<ffffffff8001d5b5>] mpage_writepages+0x1bf/0x37d
 [<ffffffff880506fd>] :ext3:ext3_ordered_writepage+0x0/0x19c
 [<ffffffff8005af83>] do_writepages+0x29/0x2f
 [<ffffffff8002ff0e>] __writeback_single_inode+0x1a2/0x31c
 [<ffffffff80021591>] sync_sb_inodes+0x1b7/0x271
 [<ffffffff800a3ab7>] keventd_create_kthread+0x0/0xc4
 [<ffffffff80051355>] writeback_inodes+0x82/0xd8
 [<ffffffff800cda21>] wb_kupdate+0xf0/0x16a
 [<ffffffff80056933>] pdflush+0x0/0x1fb
 [<ffffffff80056a84>] pdflush+0x151/0x1fb
 [<ffffffff800cd931>] wb_kupdate+0x0/0x16a
 [<ffffffff80032c2b>] kthread+0xfe/0x132
 [<ffffffff800a06db>] request_module+0x0/0x14d
 [<ffffffff8005dfc1>] child_rip+0xa/0x11
 [<ffffffff800a3ab7>] keventd_create_kthread+0x0/0xc4
 [<ffffffff80032b2d>] kthread+0x0/0x132
 [<ffffffff8005dfb7>] child_rip+0x0/0x11