I am not sure this is related with the other reports for lockups etc on 
3.16-rc1, so i am sending it. full dmesg attached. this is after some 
heavy io on a multi disk btrfs filesystem.

[69932.966704] INFO: task btrfs-transacti:516 blocked for more than 120 
seconds.
[69932.966837]       Not tainted 3.16.0-rc1-ge99cfa2 #1
[69932.966921] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" 
disables this message.
[69932.967051] btrfs-transacti D 0000000000000001     0   516      2 
0x00000000
[69932.967060]  ffff8801f422fac0 0000000000000046 ffff880203f3bd20 
00000000000145c0
[69932.967069]  ffff8801f422ffd8 00000000000145c0 ffff880203f3bd20 
ffff8801f422fa30
[69932.967076]  ffffffffa062e392 ffff8800cda63300 ffff8802010b1e60 
00000c73d1920000
[69932.967083] Call Trace:
[69932.967133]  [<ffffffffa062e392>] ? add_delayed_tree_ref+0x102/0x1b0 
[btrfs]
[69932.967146]  [<ffffffff8119937a>] ? kmem_cache_alloc_trace+0x1fa/0x220
[69932.967155]  [<ffffffff814fd759>] schedule+0x29/0x70
[69932.967179]  [<ffffffffa05c8571>] cache_block_group+0x121/0x390 [btrfs]
[69932.967187]  [<ffffffff810b0990>] ? __wake_up_sync+0x20/0x20
[69932.967212]  [<ffffffffa05d16fa>] find_free_extent+0x5fa/0xc80 [btrfs]
[69932.967243]  [<ffffffffa0606f00>] ? free_extent_buffer+0x10/0xa0 [btrfs]
[69932.967269]  [<ffffffffa05d1f52>] btrfs_reserve_extent+0x62/0x140 [btrfs]
[69932.967298]  [<ffffffffa05ed388>] 
__btrfs_prealloc_file_range+0xe8/0x380 [btrfs]
[69932.967328]  [<ffffffffa05f52b0>] 
btrfs_prealloc_file_range_trans+0x30/0x40 [btrfs]
[69932.967353]  [<ffffffffa05d4a97>] 
btrfs_write_dirty_block_groups+0x5c7/0x700 [btrfs]
[69932.967380]  [<ffffffffa05e2b5d>] commit_cowonly_roots+0x18d/0x240 
[btrfs]
[69932.967408]  [<ffffffffa05e4c87>] 
btrfs_commit_transaction+0x4f7/0xa40 [btrfs]
[69932.967435]  [<ffffffffa05e0835>] transaction_kthread+0x1e5/0x250 [btrfs]
[69932.967462]  [<ffffffffa05e0650>] ? 
btrfs_cleanup_transaction+0x570/0x570 [btrfs]
[69932.967471]  [<ffffffff8108c97b>] kthread+0xdb/0x100
[69932.967478]  [<ffffffff8108c8a0>] ? kthread_create_on_node+0x180/0x180
[69932.967486]  [<ffffffff8150137c>] ret_from_fork+0x7c/0xb0
[69932.967493]  [<ffffffff8108c8a0>] ? kthread_create_on_node+0x180/0x180
[69932.967505] INFO: task kworker/u16:15:30882 blocked for more than 120 
seconds.

-- 
Konstantinos Skarlatos