For what it's worth, here is the backtrace from when I reproduced the bug using emacs/evince.  Maybe it is helpful to look for similarities in the code path, though it certainly sounds like the crypto code in ecryptfs is the place to begin.  I may try putting in lots of WARN_ON(irqs_disabled()).

Just as a note, from disassembly it doesn't appear that the aesni_intel module contains the cli instruction, so interrupts must get disabled somewhere else.  As a wild guess, I speculate that somewhere there is a irq_enable/irq_disable pair with the possibility to erroneously jump out from the middle, and something about using the aesni_intel module makes that happen.  Maybe in the generic crypto code that only calls aesni_intel if it's available?

[  322.435871] ------------[ cut here ]------------
[  322.435925] kernel BUG at /build/buildd/linux-3.11.0/fs/buffer.c:1268!
[  322.435979] invalid opcode: 0000 [#1] SMP 
[  322.436017] Modules linked in: xt_recent michael_mic arc4 dm_crypt joydev ip6t_REJECT xt_hl ip6t_rt nf_conntrack_ipv6 nf_defrag_ipv6 ipt_REJECT xt_comment xt_LOG parport_pc ppdev lp parport xt_limit xt_tcpudp xt_addrtype nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack ip6table_filter ip6_tables nf_conntrack_netbios_ns nf_conntrack_broadcast nf_nat_ftp nf_nat nf_conntrack_ftp nf_conntrack iptable_filter ip_tables x_tables bnep rfcomm bluetooth x86_pkg_temp_thermal intel_powerclamp coretemp kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd hp_wmi sparse_keymap snd_hda_codec_hdmi snd_hda_codec_idt binfmt_misc uvcvideo videobuf2_vmalloc snd_hda_intel snd_hda_codec videobuf2_memops snd_hwdep videobuf2_core videodev snd_pcm lib80211_crypt_tkip snd_page_alloc snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq microcode wl(POF) snd_seq_device snd_timer lib80211 psmouse serio_raw cfg80211 rtsx_pci_ms snd memstick lpc_ich mei_me soundcore mei mac_hid rtsx_pci_sdmmc i915 i2c_algo_bit drm_kms_helper sdhci_pci sdhci drm ahci r8169 rtsx_pci mii libahci wmi video
[  322.437181] CPU: 3 PID: 3174 Comm: evince Tainted: PF          O 3.11.0-15-generic #23-Ubuntu
[  322.437266] Hardware name: Hewlett-Packard HP Folio 13 Notebook PC/17F8, BIOS F.0B 01/23/2013
[  322.437353] task: ffff880146af2ee0 ti: ffff880144152000 task.ti: ffff880144152000
[  322.437511] RIP: 0010:[<ffffffff816e3efd>]  [<ffffffff816e3efd>] check_irqs_on.part.11+0x4/0x6
[  322.437699] RSP: 0018:ffff8801441534c8  EFLAGS: 00010046
[  322.437805] RAX: 0000000000000086 RBX: 0000000000001000 RCX: ffff880144955800
[  322.437937] RDX: 0000000000001000 RSI: 0000000000000554 RDI: ffff88014934a3c0
[  322.438069] RBP: ffff8801441534c8 R08: 0000000000000000 R09: 0000000000000000
[  322.438186] R10: ffff880144955800 R11: 0000000000001000 R12: ffff880144153650
[  322.438262] R13: ffff8801438b9000 R14: ffff88014f8a8000 R15: ffff88014934a3c0
[  322.438338] FS:  00007feab6487a00(0000) GS:ffff88014fac0000(0000) knlGS:0000000000000000
[  322.438425] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  322.438486] CR2: 00000000021aa1b8 CR3: 0000000001c0e000 CR4: 00000000000407e0
[  322.438561] Stack:
[  322.438584]  ffff880144153538 ffffffff811d81a9 0000000000000000 0000000000000000
[  322.438672]  0000000000000000 0000000000000000 0000000000000000 0000000000000000
[  322.438757]  0000000000000000 0000000000000000 0000000000001000 ffff880144153650
[  322.438842] Call Trace:
[  322.438881]  [<ffffffff811d81a9>] __find_get_block+0x229/0x230
[  322.438948]  [<ffffffff811d81d4>] __getblk+0x24/0x2e0
[  322.439013]  [<ffffffff81241230>] __ext4_get_inode_loc+0x110/0x3d0
[  322.439084]  [<ffffffff81242f9d>] ext4_get_inode_loc+0x1d/0x20
[  322.439168]  [<ffffffff81244796>] ext4_reserve_inode_write+0x26/0xa0
[  322.439251]  [<ffffffff812479b0>] ? ext4_dirty_inode+0x40/0x60
[  322.439322]  [<ffffffff81244854>] ext4_mark_inode_dirty+0x44/0x1f0
[  322.439398]  [<ffffffff812479b0>] ext4_dirty_inode+0x40/0x60
[  322.439461]  [<ffffffff811d13b2>] __mark_inode_dirty+0x1f2/0x2f0
[  322.439529]  [<ffffffff811c0b8e>] update_time+0x8e/0xd0
[  322.439588]  [<ffffffff811c0d90>] file_update_time+0x80/0xd0
[  322.439658]  [<ffffffff81140d40>] __generic_file_aio_write+0x180/0x3d0
[  322.439730]  [<ffffffff81140fed>] generic_file_aio_write+0x5d/0xc0
[  322.439800]  [<ffffffff8123c6f9>] ext4_file_write+0x99/0x3f0
[  322.439866]  [<ffffffff811a69f0>] do_sync_write+0x80/0xb0
[  322.439927]  [<ffffffff811a712d>] vfs_write+0xbd/0x1e0
[  322.439986]  [<ffffffff811d2888>] kernel_write+0x38/0x50
[  322.440049]  [<ffffffff812aab69>] ecryptfs_write_lower+0x29/0x50
[  322.440117]  [<ffffffff812abf6c>] ecryptfs_encrypt_page+0xec/0x180
[  322.440186]  [<ffffffff812aa084>] ecryptfs_writepage+0x14/0x60
[  322.443446]  [<ffffffff81148553>] __writepage+0x13/0x40
[  322.446584]  [<ffffffff81148f31>] write_cache_pages+0x241/0x4b0
[  322.449735]  [<ffffffff81092599>] ? ttwu_do_wakeup+0x19/0xd0
[  322.453039]  [<ffffffff81148540>] ? global_dirtyable_memory+0x50/0x50
[  322.455525]  [<ffffffff811ed50b>] ? ep_poll_callback+0x11b/0x170
[  322.458577]  [<ffffffff8108977b>] ? srcu_readers_seq_idx.isra.6+0x5b/0x80
[  322.461975]  [<ffffffff816ee5be>] ? _raw_spin_lock+0xe/0x20
[  322.463799]  [<ffffffff811491e0>] generic_writepages+0x40/0x60
[  322.466051]  [<ffffffff8114a695>] do_writepages+0x35/0x40
[  322.468529]  [<ffffffff811401e9>] __filemap_fdatawrite_range+0x59/0x60
[  322.471404]  [<ffffffff8114024c>] filemap_write_and_wait+0x2c/0x60
[  322.474554]  [<ffffffff812a9d02>] ecryptfs_put_lower_file+0x32/0x60
[  322.476670]  [<ffffffff812a6fe2>] ecryptfs_release+0x12/0x30
[  322.478669]  [<ffffffff811a8be1>] __fput+0xe1/0x230
[  322.481218]  [<ffffffff811a8d7e>] ____fput+0xe/0x10
[  322.484676]  [<ffffffff810813c4>] task_work_run+0xc4/0xe0
[  322.488118]  [<ffffffff81064257>] do_exit+0x2b7/0xa40
[  322.490307]  [<ffffffff81071133>] ? __sigqueue_free.part.15+0x33/0x40
[  322.492447]  [<ffffffff81064a5f>] do_group_exit+0x3f/0xa0
[  322.494632]  [<ffffffff810742c0>] get_signal_to_deliver+0x1d0/0x5e0
[  322.496851]  [<ffffffff81012438>] do_signal+0x48/0x960
[  322.498977]  [<ffffffff815d9b0c>] ? SYSC_recvfrom+0x11c/0x160
[  322.500196]  [<ffffffff81011609>] ? __switch_to+0x169/0x4b0
[  322.502213]  [<ffffffff810913c0>] ? finish_task_switch+0x50/0xf0
[  322.504268]  [<ffffffff81012dc8>] do_notify_resume+0x78/0xa0
[  322.506307]  [<ffffffff816f74da>] int_signal+0x12/0x17
[  322.508366] Code: f0 2c a6 81 e8 b5 d9 ff ff 4d 85 e4 74 14 49 8d 7c 24 58 e8 b6 9f 96 ff 66 90 4c 89 e7 e8 bc 90 ad ff 5b 41 5c 5d c3 55 48 89 e5 <0f> 0b 55 48 89 e5 0f 0b 55 48 89 e5 0f 0b 55 48 89 e5 0f 0b 55 
[  322.513147] RIP  [<ffffffff816e3efd>] check_irqs_on.part.11+0x4/0x6
[  322.515577]  RSP <ffff8801441534c8>
[  322.526687] ---[ end trace 37836371a7bce466 ]---
[  322.526690] Fixing recursive fault but reboot is needed!