OSDs could crash with the following "assertion failed" message (crash didn't affect data
and was caused by OSD thinking upper blocks are full while they weren't). Reproduction
without introducing artificial delays is hard because you have to force OSD to read an
object with enqueued but not handled write which fills previously non-full bitmap. O_o.
```
vitastor-osd: ./src/osd/osd_primary_chain.cpp:613: void osd_t::send_chained_read_results(pg_t&, osd_op_t*): Assertion `stripes[role].read_buf' failed.
```
Vitaliy Filippov
b58bf3ada5