MDEV-23693 Failing assertion: my_atomic_load32_explicit(&lock->lock_word, MY_MEMORY_ORDER_RELAXED) == X_LOCK_DECR

InnoDB frees the block lock during buffer pool shrinking when other
thread is yet to release the block lock.  While shrinking the
buffer pool, InnoDB allows the page to be freed unless it is buffer
fixed. In some cases, InnoDB releases the latch after unfixing the
block.

Fix:
====
- InnoDB should unfix the block after releases the latch.

- Add more assertion to check buffer fix while accessing the page.

- Introduced block_hint structure to store buf_block_t pointer
and allow accessing the buf_block_t pointer only by passing a
functor. It returns original buf_block_t* pointer if it is valid
or nullptr if the pointer become stale.

- Replace buf_block_is_uncompressed() with
buf_pool_t::is_block_pointer()

This change is motivated by a change in mysql-5.7.32:
mysql/mysql-server@46e60de444a8fbd876cc6778a7e64a1d3426a48d
Bug #31036301 ASSERTION FAILURE: SYNC0RW.IC:429:LOCK->LOCK_WORD

1 files changed, 2 insertions, 2 deletions

diff --git a/storage/innobase/include/mtr0mtr.ic b/storage/innobase/include/mtr0mtr.ic
index 8d68affb1cb..a45d088d5d7 100644
--- a/storage/innobase/include/mtr0mtr.ic
+++ b/storage/innobase/include/mtr0mtr.ic
@@ -170,10 +170,10 @@ mtr_t::release_block_at_savepoint(
 
 	ut_a(slot->object == block);
 
-	buf_block_unfix(reinterpret_cast<buf_block_t*>(block));
-
 	buf_page_release_latch(block, slot->type);
 
+	buf_block_unfix(reinterpret_cast<buf_block_t*>(block));
+
 	slot->object = NULL;
 }