The file log.txt has one of many kernel message logs (logged via syslog) about 
btrfs_rename2 that happened while the laptop in question was apparently 
working OK.

The file dm.txt has part of the output of dmesg after the system got into a 
state where all disk access was going to D state, that wasn't logged via 
syslog because writing to files was impossible.

Any suggestions on what to do to further debug this?  The problem of all 
processes going to D state happens periodically, so presumably it will happen 
again soon enough.  I've got the commonly used utilities like cat, dmesg, ssh, 
etc locked in RAM so I can run them without disk access.  It appears that the 
BTRFS filesystem (which is used for all storage on the laptop) works fine as 
long there is only reads from cache.

I've tried kernel 5.2.11 but that one hangs on resume.