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    SubjectRe: [2.6.32] task hung
    On Tue, 4 May 2010 14:49:50 +0200
    Folkert van Heusden <folkert@vanheusden.com> wrote:

    > Hi,
    >
    > I'm copying 6GB of data onto an NBD device using a simple tool which
    > differs from dd/cat in that it measures how long it takes to write each
    > block and does a sync after each block.
    > Now during that run I get:
    >
    > [45480.665074] INFO: task measurecopy:13780 blocked for more than 120 seconds.
    > [45480.665086] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    > [45480.665090] measurecopy D 0000000000000000 0 13780 30341 0x00000000
    > [45480.665102] ffff8801bf06d4c0 0000000000000082 0000000000000000 ffff8801776d9d04
    > [45480.665116] 0000000000000001 ffff88000000f640 000000000000f8a0 ffff8801776d9fd8
    > [45480.665129] 00000000000155c0 00000000000155c0 ffff8801a867d4c0 ffff8801a867d7b8
    > [45480.665143] Call Trace:
    > [45480.665153] [<ffffffff8106beb9>] ? ktime_get_ts+0x68/0xb2
    > [45480.665159] [<ffffffff81098f06>] ? delayacct_end+0x74/0x7f
    > [45480.665168] [<ffffffff810b3219>] ? sync_page+0x0/0x46
    > [45480.665175] [<ffffffff812edf36>] ? io_schedule+0x73/0xb7
    > [45480.665181] [<ffffffff810b325a>] ? sync_page+0x41/0x46
    > [45480.665186] [<ffffffff812ee436>] ? __wait_on_bit+0x41/0x70
    > [45480.665192] [<ffffffff810b33de>] ? wait_on_page_bit+0x6b/0x71
    > [45480.665199] [<ffffffff81064a84>] ? wake_bit_function+0x0/0x23
    > [45480.665206] [<ffffffff810baf36>] ? pagevec_lookup_tag+0x1a/0x21
    > [45480.665212] [<ffffffff810b3bb4>] ? wait_on_page_writeback_range+0x69/0x11b
    > [45480.665218] [<ffffffff810b3d26>] ? filemap_write_and_wait_range+0x43/0x52
    > [45480.665225] [<ffffffff8110a176>] ? vfs_fsync_range+0x55/0x9e
    > [45480.665231] [<ffffffff8110a23e>] ? do_fsync+0x28/0x39
    > [45480.665236] [<ffffffff8110a25d>] ? sys_fdatasync+0xe/0x13
    > [45480.665243] [<ffffffff81010b42>] ? system_call_fastpath+0x16/0x1b
    >
    > command line:
    > ./measurecopy -i /dev/VG01/LVHOME -o /dev/nbd0 -s -b 1048576
    >
    > http://www.vanheusden.com/measurecopy/
    >
    >

    end_page_writeback() never got run against a page. My guess would be
    that NBD got its knickers in a knot.


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