Bug#471465: Info received (Bug#471465: laptop-mode-tools: mount takes 100% of CPU after unplugging AC )

[Sanjoy Mahajan <sanjoy@MIT.EDU>]

I just noticed new information in the dmesg that is probably related:

  $ dmesg | grep INFO
  [ 2501.840262] INFO: task pdflush:178 blocked for more than 120 seconds.
  [ 2632.815719] INFO: task pdflush:178 blocked for more than 120 seconds.
  [ 2762.761167] INFO: task pdflush:178 blocked for more than 120 seconds.
  [ 2895.895694] INFO: task pdflush:178 blocked for more than 120 seconds.
  [ 3034.407985] INFO: task pdflush:178 blocked for more than 120 seconds.
  [ 3167.543457] INFO: task pdflush:178 blocked for more than 120 seconds.
  [ 3304.982146] INFO: task pdflush:178 blocked for more than 120 seconds.
  [ 3438.128290] INFO: task pdflush:178 blocked for more than 120 seconds.

So, roughly every 2 minutes the system reported that pdflush was hanging
for a while.  The first INFO message happened at 8.13pm, while the
'mount' was running, as are the next few.  The last one or two might
have occured after the 'mount' finished but I'm not sure.

Here is one of the entries:

[ 2762.761167] INFO: task pdflush:178 blocked for more than 120 seconds.
[ 2762.761174] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2762.761177] pdflush       D 00000228     0   178      2
[ 2762.761182]        f749d970 00000046 51dd6d03 00000228 f749daf0 c1bfe920 00000000 c0137ba7 
[ 2762.761189]        000063db 00000000 c1bfb920 0000319c 00000000 c1bfb920 fffeffff f784283c 
[ 2762.761196]        f7739fac f749d970 c02b4fa8 f7739f50 f7842844 f7e41998 f784283c f784283c 
[ 2762.761202] Call Trace:
[ 2762.761229]  [<c0137ba7>] getnstimeofday+0x30/0xb6
[ 2762.761244]  [<c02b4fa8>] rwsem_down_failed_common+0x14c/0x167
[ 2762.761254]  [<c02b4ffc>] rwsem_down_read_failed+0x1a/0x22
[ 2762.761262]  [<c02b5067>] call_rwsem_down_read_failed+0x7/0xc
[ 2762.761268]  [<c02b4881>] down_read+0xa/0xb
[ 2762.761271]  [<c01773c7>] sync_supers+0x2e/0x8c
[ 2762.761278]  [<c015e46d>] pdflush+0x0/0x1c6
[ 2762.761283]  [<c015e107>] wb_kupdate+0x25/0xdb
[ 2762.761293]  [<c015e46d>] pdflush+0x0/0x1c6
[ 2762.761298]  [<c015e596>] pdflush+0x129/0x1c6
[ 2762.761303]  [<c015e0e2>] wb_kupdate+0x0/0xdb
[ 2762.761309]  [<c01338d5>] kthread+0x38/0x5f
[ 2762.761314]  [<c013389d>] kthread+0x0/0x5f
[ 2762.761320]  [<c010849f>] kernel_thread_helper+0x7/0x10