Hi,
I was just looking throught the current 5.4-stable queue and saw that 28553fa992cb28 ('Btrfs: fix race between shrinking truncate and fiemap') is queued. Upstream has a follow-up fix for this: 52e29e331070cd aka 'btrfs: don't set path->leave_spinning for truncate'.
Would be nice to get those in together. I only looked at 5.4, don't know about other queues.
thanks, Holger