Comment 7 for bug 1349711

I found an additional stack trace from a previous machine lockup.

[1093202.136107] INFO: task kworker/u30:1:31455 blocked for more than 120 seconds.
[1093202.141596] Tainted: GF 3.13.0-30-generic #54-Ubuntu
[1093202.146201] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[1093202.152408] kworker/u30:1 D ffff8801efc34440 0 31455 2 0x00000000
[1093202.152416] Workqueue: writeback bdi_writeback_workfn (flush-btrfs-1)
[1093202.152419] ffff880040d3b768 0000000000000002 ffff8800880f0000 ffff880040d3bfd8
[1093202.152422] 0000000000014440 0000000000014440 ffff8800880f0000 ffff8801efc34cd8
[1093202.152426] ffff8801effcefe8 ffff880040d3b7f0 0000000000000002 ffffffff8114e010
[1093202.152429] Call Trace:
[1093202.152435] [<ffffffff8114e010>] ? wait_on_page_read+0x60/0x60
[1093202.152439] [<ffffffff8171ea6d>] io_schedule+0x9d/0x140
[1093202.152442] [<ffffffff8114e01e>] sleep_on_page+0xe/0x20
[1093202.152445] [<ffffffff8171eff8>] __wait_on_bit_lock+0x48/0xb0
[1093202.152449] [<ffffffff8109df64>] ? vtime_common_task_switch+0x24/0x40
[1093202.152452] [<ffffffff8114e12a>] __lock_page+0x6a/0x70
[1093202.152456] [<ffffffff810aaee0>] ? autoremove_wake_function+0x40/0x40
[1093202.152474] [<ffffffffa00e8a0d>] lock_delalloc_pages+0x13d/0x1d0 [btrfs]
[1093202.152487] [<ffffffffa00eaf2b>] find_lock_delalloc_range.constprop.43+0x14b/0x1f0 [btrfs]
[1093202.152499] [<ffffffffa00ebfa1>] __extent_writepage+0x131/0x750 [btrfs]
[1093202.152509] [<ffffffffa00eb040>] ? end_extent_writepage+0x70/0x70 [btrfs]
[1093202.152521] [<ffffffffa00ec832>] extent_write_cache_pages.isra.30.constprop.50+0x272/0x3d0 [btrfs]
[1093202.152532] [<ffffffffa00edafd>] extent_writepages+0x4d/0x70 [btrfs]
[1093202.152544] [<ffffffffa00d3b20>] ? btrfs_real_readdir+0x5b0/0x5b0 [btrfs]
[1093202.152555] [<ffffffffa00d1cb8>] btrfs_writepages+0x28/0x30 [btrfs]
[1093202.152559] [<ffffffff8115a46e>] do_writepages+0x1e/0x40
[1093202.152562] [<ffffffff811e5c50>] __writeback_single_inode+0x40/0x210
[1093202.152565] [<ffffffff811e6a07>] writeback_sb_inodes+0x247/0x3e0
[1093202.152568] [<ffffffff811e6c3f>] __writeback_inodes_wb+0x9f/0xd0
[1093202.152571] [<ffffffff811e6eb3>] wb_writeback+0x243/0x2c0
[1093202.152574] [<ffffffff811e86d8>] bdi_writeback_workfn+0x108/0x430
[1093202.152577] [<ffffffff810974a8>] ? finish_task_switch+0x128/0x170
[1093202.152581] [<ffffffff810838a2>] process_one_work+0x182/0x450
[1093202.152585] [<ffffffff81084641>] worker_thread+0x121/0x410
[1093202.152588] [<ffffffff81084520>] ? rescuer_thread+0x3e0/0x3e0
[1093202.152591] [<ffffffff8108b322>] kthread+0xd2/0xf0
[1093202.152594] [<ffffffff8108b250>] ? kthread_create_on_node+0x1d0/0x1d0
[1093202.152598] [<ffffffff8172ac3c>] ret_from_fork+0x7c/0xb0
[1093202.152601] [<ffffffff8108b250>] ? kthread_create_on_node+0x1d0/0x1d0