Snippet from syslog.1

Last night:
=========================================

Nov  2 23:10:06 ubuntu-1 kernel: [140230.568863] ------------[ cut here ]------------
Nov  2 23:10:06 ubuntu-1 kernel: [140230.568877] WARNING: CPU: 1 PID: 11663 at /build/buildd/linux-3.13.0/fs/proc/generic.c:511 remove_proc_entry+0x139/0x1b0()
Nov  2 23:10:06 ubuntu-1 kernel: [140230.568880] name 'fs/nfsfs'
Nov  2 23:10:06 ubuntu-1 kernel: [140230.568883] Modules linked in: snd_hda_codec_hdmi bnep rfcomm kvm_amd bluetooth kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_seq_midi snd_seq_midi_event aesni_intel snd_hda_codec_realtek aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd serio_raw fam15h_power edac_core edac_mce_amd k10temp snd_hda_intel snd_hda_codec snd_hwdep nouveau snd_pcm snd_page_alloc snd_rawmidi sp5100_tco i2c_piix4 snd_seq mxm_wmi wmi video snd_seq_device ttm snd_timer drm_kms_helper parport_pc drm binfmt_misc snd ppdev i2c_algo_bit soundcore mac_hid lp parport nfsd auth_rpcgss nfs_acl nfs lockd sunrpc fscache hid_generic usbhid hid raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq raid1 firewire_ohci raid0 r8169 firewire_core mii crc_itu_t ahci multipath libahci linear
Nov  2 23:10:06 ubuntu-1 kernel: [140230.568977] CPU: 1 PID: 11663 Comm: kworker/u16:1 Tainted: G        W     3.13.0-39-generic #66-Ubuntu
Nov  2 23:10:06 ubuntu-1 kernel: [140230.568981] Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./990FXA-UD5, BIOS FB 01/23/2013
Nov  2 23:10:06 ubuntu-1 kernel: [140230.568988] Workqueue: netns cleanup_net
Nov  2 23:10:06 ubuntu-1 kernel: [140230.568992]  0000000000000009 ffff8803f8aa1c80 ffffffff8171ece7 ffff8803f8aa1cc8
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569000]  ffff8803f8aa1cb8 ffffffff8106773d 0000000000000000 0000000000000005
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569007]  ffffffffa01cd8a8 ffff88041e005ab0 0000000000000200 ffff8803f8aa1d18
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569014] Call Trace:
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569023]  [<ffffffff8171ece7>] dump_stack+0x45/0x56
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569030]  [<ffffffff8106773d>] warn_slowpath_common+0x7d/0xa0
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569039]  [<ffffffff810677ac>] warn_slowpath_fmt+0x4c/0x50
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569050]  [<ffffffff81229889>] remove_proc_entry+0x139/0x1b0
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569078]  [<ffffffffa01ad4e2>] nfs_fs_proc_net_exit+0x62/0x70 [nfs]
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569098]  [<ffffffffa01b35b2>] nfs_net_exit+0x12/0x20 [nfs]
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569104]  [<ffffffff8161b3a9>] ops_exit_list.isra.1+0x39/0x60
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569112]  [<ffffffff8161bc30>] cleanup_net+0x110/0x250
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569120]  [<ffffffff810839c2>] process_one_work+0x182/0x450
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569126]  [<ffffffff810847b1>] worker_thread+0x121/0x410
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569132]  [<ffffffff81084690>] ? rescuer_thread+0x430/0x430
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569138]  [<ffffffff8108b492>] kthread+0xd2/0xf0
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569144]  [<ffffffff8108b3c0>] ? kthread_create_on_node+0x1c0/0x1c0
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569150]  [<ffffffff8172f73c>] ret_from_fork+0x7c/0xb0
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569156]  [<ffffffff8108b3c0>] ? kthread_create_on_node+0x1c0/0x1c0
Nov  2 23:10:06 ubuntu-1 kernel: [140230.569160] ---[ end trace 19f294f7c6698bcf ]---

============================================================

And This morning after restarting the system

Nov  2 07:54:19 ubuntu-1 kernel: [85246.458920] ------------[ cut here ]------------
Nov  2 07:54:19 ubuntu-1 kernel: [85246.458934] WARNING: CPU: 1 PID: 7918 at /build/buildd/linux-3.13.0/fs/proc/generic.c:511 remove_proc_entry+0x139/0x1b0()
Nov  2 07:54:19 ubuntu-1 kernel: [85246.458938] name 'fs/nfsfs'
Nov  2 07:54:19 ubuntu-1 kernel: [85246.458940] Modules linked in: snd_hda_codec_hdmi bnep rfcomm kvm_amd bluetooth kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_seq_midi snd_seq_midi_event aesni_intel snd_hda_codec_realtek aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd serio_raw fam15h_power edac_core edac_mce_amd k10temp snd_hda_intel snd_hda_codec snd_hwdep nouveau snd_pcm snd_page_alloc snd_rawmidi sp5100_tco i2c_piix4 snd_seq mxm_wmi wmi video snd_seq_device ttm snd_timer drm_kms_helper parport_pc drm binfmt_misc snd ppdev i2c_algo_bit soundcore mac_hid lp parport nfsd auth_rpcgss nfs_acl nfs lockd sunrpc fscache hid_generic usbhid hid raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq raid1 firewire_ohci raid0 r8169 firewire_core mii crc_itu_t ahci multipath libahci linear
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459035] CPU: 1 PID: 7918 Comm: kworker/u16:0 Tainted: G        W     3.13.0-39-generic #66-Ubuntu
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459039] Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./990FXA-UD5, BIOS FB 01/23/2013
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459045] Workqueue: netns cleanup_net
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459049]  0000000000000009 ffff8803e899bc80 ffffffff8171ece7 ffff8803e899bcc8
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459057]  ffff8803e899bcb8 ffffffff8106773d 0000000000000000 0000000000000005
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459064]  ffffffffa01cd8a8 ffff88041e005ab0 0000000000000200 ffff8803e899bd18
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459071] Call Trace:
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459080]  [<ffffffff8171ece7>] dump_stack+0x45/0x56
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459088]  [<ffffffff8106773d>] warn_slowpath_common+0x7d/0xa0
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459097]  [<ffffffff810677ac>] warn_slowpath_fmt+0x4c/0x50
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459107]  [<ffffffff81229889>] remove_proc_entry+0x139/0x1b0
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459135]  [<ffffffffa01ad4e2>] nfs_fs_proc_net_exit+0x62/0x70 [nfs]
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459156]  [<ffffffffa01b35b2>] nfs_net_exit+0x12/0x20 [nfs]
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459161]  [<ffffffff8161b3a9>] ops_exit_list.isra.1+0x39/0x60
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459170]  [<ffffffff8161bc30>] cleanup_net+0x110/0x250
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459177]  [<ffffffff810839c2>] process_one_work+0x182/0x450
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459183]  [<ffffffff810847b1>] worker_thread+0x121/0x410
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459190]  [<ffffffff81084690>] ? rescuer_thread+0x430/0x430
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459196]  [<ffffffff8108b492>] kthread+0xd2/0xf0
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459202]  [<ffffffff8108b3c0>] ? kthread_create_on_node+0x1c0/0x1c0
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459208]  [<ffffffff8172f73c>] ret_from_fork+0x7c/0xb0
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459214]  [<ffffffff8108b3c0>] ? kthread_create_on_node+0x1c0/0x1c0
Nov  2 07:54:19 ubuntu-1 kernel: [85246.459218] ---[ end trace 19f294f7c6698a78 ]---