MDEV-24258 preparation: Remove dict_sys.freeze() and unfreeze()

With this change, dict_sys.latch will essentially become a mutex
(it is only acquired in exclusive mode).

The subsequent commit will merge dict_sys.mutex into dict_sys.latch
and reintroduce dict_sys.freeze() for those cases where we currently
acquire only dict_sys.latch but not dict_sys.mutex. The case where
both are acquired will be mapped to dict_sys.lock().

i_s_sys_tables_fill_table_stats(): Invoke dict_sys.prevent_eviction()
and the new function dict_sys.allow_eviction() to avoid table eviction
while a row in INFORMATION_SCHEMA.INNODB_SYS_TABLESTATS is being
produced.

3 files changed, 40 insertions, 32 deletions

diff --git a/storage/innobase/handler/i_s.cc b/storage/innobase/handler/i_s.cc
index 8d8ab582f05..3b2207beed5 100644
--- a/storage/innobase/handler/i_s.cc
+++ b/storage/innobase/handler/i_s.cc
@@ -5097,9 +5097,8 @@ i_s_sys_tables_fill_table_stats(
 		DBUG_RETURN(0);
 	}
 
-	dict_sys.freeze();
-	dict_sys.mutex_lock();
-	mtr_start(&mtr);
+	mtr.start();
+	dict_sys.lock(SRW_LOCK_CALL);
 
 	rec = dict_startscan_system(&pcur, &mtr, dict_sys.sys_tables);
 
@@ -5112,33 +5111,36 @@ i_s_sys_tables_fill_table_stats(
 		this SYS_TABLES record */
 		err_msg = i_s_sys_tables_rec(pcur, nullptr, &table_rec);
 
-		ulint ref_count = table_rec ? table_rec->get_ref_count() : 0;
-		dict_sys.mutex_unlock();
-
-		if (table_rec != NULL) {
-			ut_ad(err_msg == NULL);
+		if (UNIV_LIKELY(!err_msg)) {
+			bool evictable = dict_sys.prevent_eviction(table_rec);
+			ulint ref_count = table_rec->get_ref_count();
+			dict_sys.unlock();
 			i_s_dict_fill_sys_tablestats(thd, table_rec, ref_count,
 						     tables->table);
+			if (!evictable) {
+				table_rec = nullptr;
+			}
 		} else {
-			ut_ad(err_msg != NULL);
+			ut_ad(!table_rec);
+			dict_sys.unlock();
 			push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
 					    ER_CANT_FIND_SYSTEM_REC, "%s",
 					    err_msg);
 		}
 
-		dict_sys.unfreeze();
-
 		/* Get the next record */
-		dict_sys.freeze();
-		dict_sys.mutex_lock();
+		mtr.start();
+		dict_sys.lock(SRW_LOCK_CALL);
+
+		if (table_rec) {
+			dict_sys.allow_eviction(table_rec);
+		}
 
-		mtr_start(&mtr);
 		rec = dict_getnext_system(&pcur, &mtr);
 	}
 
-	mtr_commit(&mtr);
-	dict_sys.mutex_unlock();
-	dict_sys.unfreeze();
+	mtr.commit();
+	dict_sys.unlock();
 
 	DBUG_RETURN(0);
 }
diff --git a/storage/innobase/include/dict0dict.h b/storage/innobase/include/dict0dict.h
index 3c0e93edc8f..6f5d2377b07 100644
--- a/storage/innobase/include/dict0dict.h
+++ b/storage/innobase/include/dict0dict.h
@@ -1527,17 +1527,28 @@ public:
   }
 #endif
 
-  /** Move a table to the non-LRU list from the LRU list. */
-  void prevent_eviction(dict_table_t *table)
+  /** Move a table to the non-LRU list from the LRU list.
+  @return whether the table was evictable */
+  bool prevent_eviction(dict_table_t *table)
   {
     ut_ad(find(table));
-    if (table->can_be_evicted)
-    {
-      table->can_be_evicted= false;
-      UT_LIST_REMOVE(table_LRU, table);
-      UT_LIST_ADD_LAST(table_non_LRU, table);
-    }
+    if (!table->can_be_evicted)
+      return false;
+    table->can_be_evicted= false;
+    UT_LIST_REMOVE(table_LRU, table);
+    UT_LIST_ADD_LAST(table_non_LRU, table);
+    return true;
   }
+  /** Move a table from the non-LRU list to the LRU list. */
+  void allow_eviction(dict_table_t *table)
+  {
+    ut_ad(find(table));
+    ut_ad(!table->can_be_evicted);
+    table->can_be_evicted= true;
+    UT_LIST_REMOVE(table_non_LRU, table);
+    UT_LIST_ADD_LAST(table_LRU, table);
+  }
+
   /** Acquire a reference to a cached table. */
   inline void acquire(dict_table_t *table);
 
@@ -1582,11 +1593,6 @@ public:
     latch.wr_unlock();
   }
 
-  /** Prevent modifications of the data dictionary */
-  void freeze() { latch.rd_lock(SRW_LOCK_CALL); ut_ad(!latch_ex); }
-  /** Allow modifications of the data dictionary */
-  void unfreeze() { ut_ad(!latch_ex); latch.rd_unlock(); }
-
   /** Estimate the used memory occupied by the data dictionary
   table and index objects.
   @return number of bytes occupied */
diff --git a/storage/innobase/row/row0upd.cc b/storage/innobase/row/row0upd.cc
index f10449b735b..41cae945c99 100644
--- a/storage/innobase/row/row0upd.cc
+++ b/storage/innobase/row/row0upd.cc
@@ -157,7 +157,7 @@ wsrep_row_upd_index_is_foreign(
   /* No MDL protects dereferencing the members of table->foreign_set. */
   const bool no_lock= !trx->dict_operation_lock_mode;
   if (no_lock)
-    dict_sys.freeze();
+    dict_sys.mutex_lock();
 
   auto end= table->foreign_set.end();
   const bool is_referenced= end !=
@@ -165,7 +165,7 @@ wsrep_row_upd_index_is_foreign(
                  [index](const dict_foreign_t* f)
                  {return f->foreign_index == index;});
   if (no_lock)
-    dict_sys.unfreeze();
+    dict_sys.mutex_unlock();
 
   return is_referenced;
 }