btrfs kernel trace 3.5.0-28-lowlatency

Apr 26 18:14:35 ewzw032 kernel: [383785.586545] ------------[ cut here ]------------
Apr 26 18:14:35 ewzw032 kernel: [383785.586567] WARNING: at fs/btrfs/free-space-cache.c:922 __btrfs_write_out_cache+0x6b9/0x990 [btrfs]()
Apr 26 18:14:35 ewzw032 kernel: [383785.586568] Hardware name: HP Compaq dc5800 Microtower
Apr 26 18:14:35 ewzw032 kernel: [383785.586570] Modules linked in: btrfs zlib_deflate libcrc32c des_generic md4 nvidia(PO) snd_hda_codec_analog arc4 tpm_infineon coretemp snd_hda_intel rtl8192cu snd_hda_codec kvm_intel rtl8192c_common rtlwifi kvm snd_hwdep snd_pcm parport_pc snd_seq_midi bnep rfcomm mac80211 ppdev snd_rawmidi bluetooth snd_seq_midi_event snd_seq binfmt_misc snd_timer snd_seq_device cfg80211 dm_multipath psmouse hp_wmi snd scsi_dh gpio_ich sparse_keymap soundcore microcode serio_raw tpm_tis mei mac_hid snd_page_alloc wmi lpc_ich lp parport nls_utf8 cifs fscache ext2 hid_generic usbhid hid usb_storage floppy e1000e
Apr 26 18:14:35 ewzw032 kernel: [383785.586607] Pid: 25834, comm: btrfs Tainted: P           O 3.5.0-28-lowlatency #31-Ubuntu
Apr 26 18:14:35 ewzw032 kernel: [383785.586608] Call Trace:
Apr 26 18:14:35 ewzw032 kernel: [383785.586615]  [<ffffffff81053d5f>] warn_slowpath_common+0x7f/0xc0
Apr 26 18:14:35 ewzw032 kernel: [383785.586617]  [<ffffffff81053dba>] warn_slowpath_null+0x1a/0x20
Apr 26 18:14:35 ewzw032 kernel: [383785.586627]  [<ffffffffa0f83fd9>] __btrfs_write_out_cache+0x6b9/0x990 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586634]  [<ffffffffa0f29325>] ? __find_space_info+0x85/0xa0 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586638]  [<ffffffff8168f76e>] ? _raw_spin_unlock+0xe/0x40
Apr 26 18:14:35 ewzw032 kernel: [383785.586646]  [<ffffffffa0f32fbc>] ? btrfs_run_delayed_refs+0x1ec/0x470 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586656]  [<ffffffffa0f84345>] btrfs_write_out_cache+0x95/0xf0 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586664]  [<ffffffffa0f3375f>] btrfs_write_dirty_block_groups+0x51f/0x5f0 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586673]  [<ffffffffa0f9edc2>] commit_cowonly_roots+0xfd/0x1c7 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586683]  [<ffffffffa0f94121>] ? btrfs_run_delayed_items+0xd1/0x150 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586692]  [<ffffffffa0f44725>] btrfs_commit_transaction+0x5d5/0xb00 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586695]  [<ffffffff81078ff0>] ? finish_wait+0x80/0x80
Apr 26 18:14:35 ewzw032 kernel: [383785.586698]  [<ffffffff8119f122>] ? __d_instantiate+0xd2/0x110
Apr 26 18:14:35 ewzw032 kernel: [383785.586701]  [<ffffffff812bf11b>] ? security_d_instantiate+0x1b/0x30
Apr 26 18:14:35 ewzw032 kernel: [383785.586710]  [<ffffffffa0f9f8ab>] create_subvol+0x4d1/0x4f8 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586720]  [<ffffffffa0f794e5>] btrfs_mksubvol+0x3a5/0x400 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586730]  [<ffffffffa0f795fe>] btrfs_ioctl_snap_create_transid+0xbe/0x180 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586740]  [<ffffffffa0f79716>] btrfs_ioctl_snap_create+0x56/0x80 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586750]  [<ffffffffa0f7baba>] btrfs_ioctl+0xc0a/0x1280 [btrfs]
Apr 26 18:14:35 ewzw032 kernel: [383785.586753]  [<ffffffff81692b84>] ? do_page_fault+0x1b4/0x4b0
Apr 26 18:14:35 ewzw032 kernel: [383785.586755]  [<ffffffff8119b307>] do_vfs_ioctl+0x97/0x530
Apr 26 18:14:35 ewzw032 kernel: [383785.586758]  [<ffffffff811898c5>] ? vfs_write+0x105/0x180
Apr 26 18:14:35 ewzw032 kernel: [383785.586760]  [<ffffffff8119b839>] sys_ioctl+0x99/0xa0
Apr 26 18:14:35 ewzw032 kernel: [383785.586762]  [<ffffffff8169081e>] ? do_device_not_available+0xe/0x10
Apr 26 18:14:35 ewzw032 kernel: [383785.586764]  [<ffffffff816969e9>] system_call_fastpath+0x16/0x1b
Apr 26 18:14:35 ewzw032 kernel: [383785.586766] ---[ end trace fadd80d2b7f6ec9f ]---