MDEV-32899 InnoDB is holding shared dict_sys.latch while waiting for FOREIGN...

MDEV-32899 InnoDB is holding shared dict_sys.latch while waiting for FOREIGN KEY child table lock on DDL

lock_table_children(): A new function to lock all child tables of a table.
We will only hold dict_sys.latch while traversing
dict_table_t::referenced_set. To prevent a race condition with
std::set::erase() we will copy the pointers to the child tables to a
local vector. Once we have acquired references to all child tables,
we can safely release dict_sys.latch, wait for the locks, and finally
release the references.

This fixes up commit 2ca11234 (MDEV-26217)
and commit c3c53926 (MDEV-26554).

storage/innobase/handler/ha_innodb.cc

@@ -13561,14 +13561,7 @@ int ha_innobase::delete_table(const char *name)
       /* FOREIGN KEY constraints cannot exist on partitioned tables. */;
 #endif
     else
-    {
-      dict_sys.freeze(SRW_LOCK_CALL);
-      for (const dict_foreign_t* f : table->referenced_set)
-        if (dict_table_t* child= f->foreign_table)
-          if ((err= lock_table_for_trx(child, trx, LOCK_X)) != DB_SUCCESS)
-            break;
-      dict_sys.unfreeze();
-    }
+      err= lock_table_children(table, trx);
   }
 
   dict_table_t *table_stats= nullptr, *index_stats= nullptr;
@@ -13966,14 +13959,7 @@ int ha_innobase::truncate()
   dict_table_t *table_stats = nullptr, *index_stats = nullptr;
   MDL_ticket *mdl_table = nullptr, *mdl_index = nullptr;
 
-  dberr_t error= DB_SUCCESS;
-
-  dict_sys.freeze(SRW_LOCK_CALL);
-  for (const dict_foreign_t *f : ib_table->referenced_set)
-    if (dict_table_t *child= f->foreign_table)
-      if ((error= lock_table_for_trx(child, trx, LOCK_X)) != DB_SUCCESS)
-        break;
-  dict_sys.unfreeze();
+  dberr_t error= lock_table_children(ib_table, trx);
 
   if (error == DB_SUCCESS)
     error= lock_table_for_trx(ib_table, trx, LOCK_X);
@@ -14164,16 +14150,7 @@ ha_innobase::rename_table(
 		/* There is no need to lock any FOREIGN KEY child tables. */
 	} else if (dict_table_t *table = dict_table_open_on_name(
 		    norm_from, false, DICT_ERR_IGNORE_FK_NOKEY)) {
-		dict_sys.freeze(SRW_LOCK_CALL);
-		for (const dict_foreign_t* f : table->referenced_set) {
-			if (dict_table_t* child = f->foreign_table) {
-				error = lock_table_for_trx(child, trx, LOCK_X);
-				if (error != DB_SUCCESS) {
-					break;
-				}
-			}
-		}
-		dict_sys.unfreeze();
+		error = lock_table_children(table, trx);
 		if (error == DB_SUCCESS) {
 			error = lock_table_for_trx(table, trx, LOCK_X);
 		}

storage/innobase/handler/handler0alter.cc

@@ -11200,16 +11200,7 @@ ha_innobase::commit_inplace_alter_table(
 			fts_optimize_remove_table(ctx->old_table);
 		}
 
-		dict_sys.freeze(SRW_LOCK_CALL);
-		for (auto f : ctx->old_table->referenced_set) {
-			if (dict_table_t* child = f->foreign_table) {
-				error = lock_table_for_trx(child, trx, LOCK_X);
-				if (error != DB_SUCCESS) {
-					break;
-				}
-			}
-		}
-		dict_sys.unfreeze();
+		error = lock_table_children(ctx->old_table, trx);
 
 		if (ctx->new_table->fts) {
 			ut_ad(!ctx->new_table->fts->add_wq);

storage/innobase/include/lock0lock.h

@@ -438,6 +438,13 @@ dberr_t lock_table_for_trx(dict_table_t *table, trx_t *trx, lock_mode mode,
                            bool no_wait= false)
 	MY_ATTRIBUTE((nonnull, warn_unused_result));
 
+/** Lock the child tables of a table.
+@param table    parent table
+@param trx      transaction
+@return error code */
+dberr_t lock_table_children(dict_table_t *table, trx_t *trx)
+	MY_ATTRIBUTE((nonnull, warn_unused_result));
+
 /** Exclusively lock the data dictionary tables.
 @param trx  dictionary transaction
 @return error code

storage/innobase/lock/lock0lock.cc

@@ -3976,6 +3976,36 @@ dberr_t lock_table_for_trx(dict_table_t *table, trx_t *trx, lock_mode mode,
   return err;
 }
 
+/** Lock the child tables of a table.
+@param table    parent table
+@param trx      transaction
+@return error code */
+dberr_t lock_table_children(dict_table_t *table, trx_t *trx)
+{
+  dict_sys.freeze(SRW_LOCK_CALL);
+  std::vector<dict_table_t*> children;
+
+  for (auto f : table->referenced_set)
+    if (dict_table_t *child= f->foreign_table)
+    {
+      child->acquire();
+      children.emplace_back(child);
+    }
+  dict_sys.unfreeze();
+
+  dberr_t err= DB_SUCCESS;
+
+  for (auto child : children)
+    if ((err= lock_table_for_trx(child, trx, LOCK_X)) != DB_SUCCESS)
+      break;
+
+  for (auto child : children)
+    child->release();
+
+  return err;
+}
+
+
 /** Exclusively lock the data dictionary tables.
 @param trx  dictionary transaction
 @return error code