The bug is due to underflow calculating the projected number of pgs - we should avoid this pg_num check at all when we're decreasing the size of a pool.
projected += pg_num * size;
projected -= pg_info.get_pg_num_target() * pg_info.get_size();
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (Red Hat Ceph Storage 6.0 Bug Fix update), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.