kernel panic when running `blkid -o full` on eoan

[Dan Watkins]

In the curtin integration tests, we have seen this kernel panic in the last of our three daily runs (unfortunately we don't have history before that):

[ 94.443649] cloud-init[1011]: Running command ['blkid', '-o', 'full'] with allowed return codes [0] (capture=True)
[ 244.975645] INFO: task blkid:4126 blocked for more than 120 seconds.
[ 244.976904] Tainted: P O 5.3.0-55-generic #49-Ubuntu
[ 244.977997] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 244.979367] blkid D 0 4126 2165 0x00004000
[ 244.980331] Call Trace:
[ 244.980810] __schedule+0x2b9/0x6c0
[ 244.981384] ? __switch_to_asm+0x40/0x70
[ 244.982038] ? __switch_to_asm+0x40/0x70
[ 244.982766] schedule+0x42/0xb0
[ 244.983284] schedule_timeout+0x203/0x2f0
[ 244.983977] wait_for_completion+0xb1/0x120
[ 244.984696] ? wake_up_q+0x70/0x70
[ 244.985272] __floppy_read_block_0+0x140/0x190 [floppy]
[ 244.986115] ? floppy_cmos_show+0x30/0x30 [floppy]
[ 244.986951] floppy_revalidate+0xfc/0x240 [floppy]
[ 244.987773] check_disk_change+0x62/0x70
[ 244.988438] floppy_open+0x28e/0x360 [floppy]
[ 244.989154] ? disk_block_events+0x5c/0x80
[ 244.989823] __blkdev_get+0xe1/0x550
[ 244.990443] blkdev_get+0x3d/0x140
[ 244.991026] ? blkdev_get_by_dev+0x50/0x50
[ 244.991711] blkdev_open+0x97/0xf0
[ 244.992305] do_dentry_open+0x143/0x3a0
[ 244.992934] vfs_open+0x2d/0x30
[ 244.993485] do_last+0x194/0x8f0
[ 244.994014] path_openat+0x8d/0x270
[ 244.994632] do_filp_open+0x91/0x100
[ 244.995231] ? __alloc_fd+0x46/0x150
[ 244.995847] do_sys_open+0x17e/0x290
[ 244.996457] __x64_sys_openat+0x20/0x30
[ 244.997091] do_syscall_64+0x5a/0x130
[ 244.997691] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 244.998552] RIP: 0033:0x7f9eb1c71fdb
[ 244.999162] Code: Bad RIP value.
[ 244.999708] RSP: 002b:00007ffffb8305e0 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
[ 245.000985] RAX: ffffffffffffffda RBX: 000055e7daa0c500 RCX: 00007f9eb1c71fdb
[ 245.002139] RDX: 0000000000080000 RSI: 000055e7daa0d680 RDI: 00000000ffffff9c
[ 245.003332] RBP: 000055e7daa0d680 R08: 0000000000000000 R09: 00007f9eb1d4bc10
[ 245.004486] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000080000
[ 245.005660] R13: 00007f9eb1da83c4 R14: 00000000dededefa R15: 0000000000000000
[ 245.006859] NMI backtrace for cpu 1
[ 245.007430] CPU: 1 PID: 25 Comm: khungtaskd Tainted: P O 5.3.0-55-generic #49-Ubuntu
[ 245.008870] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[ 245.010326] Call Trace:
[ 245.010794] dump_stack+0x6d/0x9a
[ 245.011344] ? lapic_can_unplug_cpu.cold+0x40/0x40
[ 245.012151] nmi_cpu_backtrace.cold+0x14/0x53
[ 245.012856] nmi_trigger_cpumask_backtrace+0xe8/0xea
[ 245.013657] arch_trigger_cpumask_backtrace+0x19/0x20
[ 245.014552] watchdog+0x32e/0x390
[ 245.015111] kthread+0x104/0x140
[ 245.015638] ? hungtask_pm_notify+0x40/0x40
[ 245.016316] ? kthread_park+0x80/0x80
[ 245.016911] ret_from_fork+0x35/0x40
[ 245.017527] Sending NMI from CPU 1 to CPUs 0:
[ 245.018311] NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xe/0x10
[ 245.019262] Kernel panic - not syncing: hung_task: blocked tasks
[ 245.020616] CPU: 1 PID: 25 Comm: khungtaskd Tainted: P O 5.3.0-55-generic #49-Ubuntu
[ 245.022109] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[ 245.023603] Call Trace:
[ 245.024021] dump_stack+0x6d/0x9a
[ 245.024554] panic+0x101/0x2d7
[ 245.025070] watchdog+0x33a/0x390
[ 245.025616] kthread+0x104/0x140
[ 245.026135] ? hungtask_pm_notify+0x40/0x40
[ 245.026851] ? kthread_park+0x80/0x80
[ 245.027470] ret_from_fork+0x35/0x40
[ 245.028131] Kernel Offset: 0x20e00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)