I was not able to reproduce this bug by running the individual tests suggested in comments #11 and #13.  However, it seems I can reproduce the hang by running the full test-storage test suite, by running: 'test-storage' and keeping all menu options enabled.

It appears some type of deadlock is happening in the kernel, since my existing terminals still accept a carriage return, but then lock up if I run a command such as top.  Here is the output I see from the test when the hang happens:



-------------[ Running job 67 / 97. Estimated time left: unknown ]--------------
------------------[ Disk stress_ng test for PERC_H355_Front ]-------------------
ID: com.canonical.certification::disk/disk_stress_ng_sda
Category: com.canonical.plainbox::disk
... 8< -------------------------------------------------------------------------
STRESS_NG_DISK_TIME env var is not found, stress_ng disk running time is default value
stress-ng: info:  [3340418] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3340418] dispatching hogs: 96 aio
stress-ng: info:  [3340418] successful run completed in 240.43s (4 mins, 0.43 secs)
stress-ng: info:  [3340616] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3340616] dispatching hogs: 96 aiol
stress-ng: info:  [3340616] successful run completed in 240.14s (4 mins, 0.14 secs)
stress-ng: info:  [3342731] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3342731] dispatching hogs: 96 chdir
stress-ng: info:  [3342731] successful run completed in 251.67s (4 mins, 11.67 secs)
stress-ng: info:  [3342828] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3342828] dispatching hogs: 96 chmod
stress-ng: info:  [3342828] successful run completed in 240.01s (4 mins, 0.01 secs)
stress-ng: info:  [3342931] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3342931] dispatching hogs: 96 chown
stress-ng: info:  [3342931] successful run completed in 240.01s (4 mins, 0.01 secs)
stress-ng: info:  [3343029] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3343029] dispatching hogs: 96 dentry
stress-ng: info:  [3343030] stress-ng-dentry: 5597426 dentries allocated
stress-ng: info:  [3343029] successful run completed in 246.89s (4 mins, 6.89 secs)
stress-ng: info:  [3343131] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3343131] dispatching hogs: 96 dir
stress-ng: info:  [3343131] successful run completed in 245.69s (4 mins, 5.69 secs)
stress-ng: info:  [3343230] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3343230] dispatching hogs: 96 fallocate
stress-ng: info:  [3343230] successful run completed in 240.04s (4 mins, 0.04 secs)
stress-ng: info:  [3343328] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3343328] dispatching hogs: 96 fiemap
stress-ng: info:  [3343815] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3343815] dispatching hogs: 96 filename
stress-ng: info:  [3343921] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3343921] dispatching hogs: 96 flock
stress-ng: info:  [3344022] setting to a 240 second (4 mins, 0.00 secs) run per stressor
stress-ng: info:  [3344022] dispatching hogs: 96 fstat

I'll investigate further.