Comment 4 for bug 1357295

Confirmed it's still happening with an updated kernel:

| [ 241.558831] INFO: task bcache_writebac:501 blocked for more than 120 seconds.
| [ 241.648361] Not tainted 3.13.0-34-generic #60-Ubuntu
| [ 241.717161] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
| [ 241.815456] bcache_writebac D ffff88303f914440 0 501 2 0x00000000
| [ 241.815464] ffff882fb6bfdeb8 0000000000000002 ffff882fb64097f0 ffff882fb6bfdfd8
| [ 241.815472] 0000000000014440 0000000000014440 ffff882fb64097f0 ffff882fb75a8bc0
| [ 241.815478] ffff882fb6be0000 ffffffffa019d840 0000000000000000 0000000000000000
| [ 241.815486] Call Trace:
| [ 241.815532] [<ffffffffa019d840>] ? read_dirty+0x400/0x400 [bcache]
| [ 241.815543] [<ffffffff817201b9>] schedule+0x29/0x70
| [ 241.815556] [<ffffffff8108b3ad>] kthread+0xad/0xf0
| [ 241.815562] [<ffffffff8108b300>] ? kthread_create_on_node+0x1d0/0x1d0
| [ 241.815573] [<ffffffff8172c6bc>] ret_from_fork+0x7c/0xb0
| [ 241.815578] [<ffffffff8108b300>] ? kthread_create_on_node+0x1d0/0x1d0

| hloeung@meteor:/var/log$ uname -a
| Linux meteor 3.13.0-34-generic #60-Ubuntu SMP Wed Aug 13 15:45:27 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

| filename: /lib/modules/3.13.0-34-generic/kernel/drivers/md/bcache/bcache.ko
| author: Kent Overstreet <email address hidden>
| license: GPL
| license: GPL
| author: Kent Overstreet <email address hidden>
| srcversion: 92E6FEAECBE61D83D1F2C4F
| depends:
| intree: Y
| vermagic: 3.13.0-34-generic SMP mod_unload modversions
| signer: Magrathea: Glacier signing key
| sig_key: 50:0B:C5:C8:7D:4B:11:5C:F3:C1:50:4F:7A:92:E2:33:C6:14:3D:58
| sig_hashalgo: sha512