While running a locally modified fsfuzzer against ecryptfs (patches going to the
fsfuzzer maintainer RSN), I accidentally didn't notice things hadn't been
unmounted, and fsfuzzer went ahead and started reformatting the underlying file
system:

# ./fsfuzz ecryptfs
Starting fsfuzz 0.7

Clearing ring buff
++ Starting Linux file-system fuzzing...
++ Current filesystem: ecryptfs
+++ Making base image
Using block size of 2048
Using filesystem size of 16 Megs
fs/ecryptfs.base is mounted; mke2fs forced anyway.  Hope /etc/mtab is incorrect.
[...boom...]

Resulting spew:

NMI Watchdog detected LOCKUP on CPU 1
CPU 1 
Modules linked in: md5 aes_generic aes_x86_64 ecryptfs(U) loop ipv6 xfrm_nalgo
crypto_api autofs4 hidp l2cap bluetooth sunrpc ip_conntrack_netbios_ns
ipt_REJECT xt_state ip_conntrack nfnetlink xt_tcpudp iptable_filter ip_tables
x_tables dm_mirror dm_multipath dm_mod video sbs backlight i2c_ec button battery
asus_acpi acpi_memhotplug ac lp sg snd_intel8x0 snd_ac97_codec ac97_bus
snd_seq_dummy snd_seq_oss parport_pc snd_seq_midi_event ide_cd snd_seq floppy
snd_seq_device parport shpchp snd_pcm_oss snd_mixer_oss i2c_i801 snd_pcm
e752x_edac i2c_core e1000 cdrom serio_raw netxen_nic snd_timer snd soundcore
edac_mc pcspkr snd_page_alloc ata_piix libata sd_mod scsi_mod ext3 jbd uhci_hcd
ohci_hcd ehci_hcd
Pid: 5517, comm: mke2fs Tainted: G      2.6.18-94.el5.bz448787 #1
RIP: 0010:[<ffffffff80064b54>]  [<ffffffff80064b54>] .text.lock.spinlock+0x2/0x30
RSP: 0018:ffff8100292a9e18  EFLAGS: 00000086
RAX: ffffffff8039f480 RBX: ffffffff8040f400 RCX: 0000000000000004
RDX: 0000000000000000 RSI: ffff8100292a9ea8 RDI: ffffffff8040f400
RBP: ffff8100292a9e40 R08: 0000000000000005 R09: 00000000ffffffe9
R10: ffffffff8012006e R11: ffffff9c3f0009c0 R12: ffffffff8040f400
R13: ffff8100292a9ea8 R14: ffff81003f610040 R15: 0000000000000000
FS:  00002b81410665f0(0000) GS:ffff81003fe667c0(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00002b8144635000 CR3: 000000002d9c7000 CR4: 00000000000006e0
Process mke2fs (pid: 5517, threadinfo ffff8100292a8000, task ffff81003f610040)
Stack:  ffffffff8008a52c 0000000000000001 0000000000000005 ffff81003f610040
 0000000000000400 ffff8100292a9ee0 ffffffff8004648e 00000000001bc03a
 0000000000000001 00000000000081a4 0000000000000000 0000000000008000
Call Trace:
 [<ffffffff8008a52c>] task_rq_lock+0x3d/0x6f
 [<ffffffff8004648e>] try_to_wake_up+0x27/0x418
 [<ffffffff80096940>] signal_wake_up+0x1e/0x2d
 [<ffffffff80097430>] specific_send_sig_info+0xa1/0xac
 [<ffffffff8009769e>] force_sig_info+0x96/0xb9
 [<ffffffff8005d312>] int_very_careful+0x35/0x3f


Code: 83 3f 00 7e f9 e9 7f fe ff ff f3 90 83 3f 00 7e f9 e9 f9 fe 
BUG: warning at arch/x86_64/kernel/crash.c:148/nmi_shootdown_cpus() (Tainted: G
    )

Call Trace:
 <NMI>  [<ffffffff80079b30>] machine_crash_shutdown+0xaa/0xf3
 [<ffffffff800aaa96>] crash_kexec+0xcc/0xe8
 [<ffffffff8012006e>] selinux_file_alloc_security+0x2a/0x53
 [<ffffffff80064b54>] .text.lock.spinlock+0x2/0x30
 [<ffffffff800651fd>] die_nmi+0x46/0xa3
 [<ffffffff800658a1>] nmi_watchdog_tick+0x107/0x1fb
 [<ffffffff80065586>] default_do_nmi+0x86/0x214
 [<ffffffff800659d8>] do_nmi+0x43/0x61
 [<ffffffff80064e47>] nmi+0x7f/0x88
 [<ffffffff8012006e>] selinux_file_alloc_security+0x2a/0x53
 [<ffffffff80064b54>] .text.lock.spinlock+0x2/0x30
 <<EOE>>  [<ffffffff8008a52c>] task_rq_lock+0x3d/0x6f
 [<ffffffff8004648e>] try_to_wake_up+0x27/0x418
 [<ffffffff80096940>] signal_wake_up+0x1e/0x2d
 [<ffffffff80097430>] specific_send_sig_info+0xa1/0xac
 [<ffffffff8009769e>] force_sig_info+0x96/0xb9
 [<ffffffff8005d312>] int_very_careful+0x35/0x3f


Nothing there is particularly ecryptfs-specific though. Not sure if this should
be considered a bug or just a "don't poke yourself like that and it won't hurt"...