Problem happens with btrfsprogs 4.19.1 https://bugzilla.kernel.org/show_bug.cgi?id=202717
That bug report includes the trace in user space; but I've also processed the resulting coredump file with gdb and attached that to the bug report. Before using --clear-space-cache v1, btrfs scrub and btrfs check came up clean no errors. Following the crash, I compiled brfsprogs 4.20.2 and ran 'btrfs check' which finds corruption. I've taken no further action, and the btrfs check output gives me no useful plain language information what the next steps are. So I'm just gonna leave it alone since it's a backup volume anyway. -- Chris Murphy
