MDEV-31816 buf_LRU_free_page() does not preserve ROW_FORMAT=COMPRESSE…

…D block state

buf_LRU_free_page(): When we are discarding the uncompressed copy of a
ROW_FORMAT=COMPRESSED page, buf_page_t::can_relocate() must have ensured
that the block descriptor state is one of FREED, UNFIXED, REINIT.
Do not overwrite the state with UNFIXED. We do not want to write back
pages that were actually freed, and we want to avoid doublewrite for
pages that were (re)initialized by log records written since the latest
checkpoint. Last but not least, we do not want crashes like those that
commit dc1bd18 (MDEV-31386)
was supposed to fix.

The test innodb_zip.wl5522_zip should typically cover all 3 states.

This bug is a regression due to
commit aaef2e1 (MDEV-27058).

storage/innobase/buf/buf0lru.cc

@@ -851,7 +851,12 @@ bool buf_LRU_free_page(buf_page_t *bpage, bool zip)
 		mysql_mutex_lock(&buf_pool.flush_list_mutex);
 		new (b) buf_page_t(*bpage);
 		b->frame = nullptr;
-		b->set_state(buf_page_t::UNFIXED + 1);
+		{
+			ut_d(uint32_t s=) b->fix();
+			ut_ad(s == buf_page_t::FREED
+			      || s == buf_page_t::UNFIXED
+			      || s == buf_page_t::REINIT);
+		}
 		break;
 	default:
 		if (zip || !bpage->zip.data || !bpage->frame) {