MDEV-18256 Duplicated call to dict_foreign_remove_from_cache()

ha_innobase::prepare_inplace_alter_table(): Filter out duplicates
from ha_alter_info->alter_info->drop_list.elements.

mysql-test/suite/innodb/r/foreign_key.result

@@ -61,3 +61,12 @@ ALTER TABLE t1 ADD pk INT NOT NULL AUTO_INCREMENT PRIMARY KEY;
 ALTER TABLE t1 CHANGE COLUMN a b TIME;
 SET SESSION FOREIGN_KEY_CHECKS = ON;
 DROP TABLE t1;
+#
+# MDEV-18256 InnoDB: Failing assertion: heap->magic_n == MEM_BLOCK_MAGIC_N
+# upon DROP FOREIGN KEY
+#
+CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t2 (b INT PRIMARY KEY, FOREIGN KEY fk1 (b) REFERENCES t1 (a))
+ENGINE=InnoDB;
+ALTER TABLE t2 DROP FOREIGN KEY fk1, DROP FOREIGN KEY fk1;
+DROP TABLE t2, t1;

mysql-test/suite/innodb/t/foreign_key.test

@@ -86,3 +86,13 @@ ALTER TABLE t1 ADD pk INT NOT NULL AUTO_INCREMENT PRIMARY KEY;
 ALTER TABLE t1 CHANGE COLUMN a b TIME;
 SET SESSION FOREIGN_KEY_CHECKS = ON;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-18256 InnoDB: Failing assertion: heap->magic_n == MEM_BLOCK_MAGIC_N
+--echo # upon DROP FOREIGN KEY
+--echo #
+CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t2 (b INT PRIMARY KEY, FOREIGN KEY fk1 (b) REFERENCES t1 (a))
+ENGINE=InnoDB;
+ALTER TABLE t2 DROP FOREIGN KEY fk1, DROP FOREIGN KEY fk1;
+DROP TABLE t2, t1;

storage/innobase/handler/handler0alter.cc

@@ -3690,12 +3690,14 @@ ha_innobase::prepare_inplace_alter_table(
 				continue;
 			}
 
+			dict_foreign_t* foreign;
+
 			for (dict_foreign_set::iterator it
 				= prebuilt->table->foreign_set.begin();
 			     it != prebuilt->table->foreign_set.end();
 			     ++it) {
 
-				dict_foreign_t*	foreign = *it;
+				foreign = *it;
 				const char* fid = strchr(foreign->id, '/');
 
 				DBUG_ASSERT(fid);
@@ -3706,7 +3708,6 @@ ha_innobase::prepare_inplace_alter_table(
 
 				if (!my_strcasecmp(system_charset_info,
 						   fid, drop->name)) {
-					drop_fk[n_drop_fk++] = foreign;
 					goto found_fk;
 				}
 			}
@@ -3715,12 +3716,19 @@ ha_innobase::prepare_inplace_alter_table(
 				 drop->name);
 			goto err_exit;
 found_fk:
+			for (ulint i = n_drop_fk; i--; ) {
+				if (drop_fk[i] == foreign) {
+					goto dup_fk;
+				}
+			}
+			drop_fk[n_drop_fk++] = foreign;
+dup_fk:
 			continue;
 		}
 
 		DBUG_ASSERT(n_drop_fk > 0);
 		DBUG_ASSERT(n_drop_fk
-			    == ha_alter_info->alter_info->drop_list.elements);
+			    <= ha_alter_info->alter_info->drop_list.elements);
 	} else {
 		drop_fk = NULL;
 	}
@@ -5057,7 +5065,7 @@ commit_try_rebuild(
 		      & Alter_inplace_info::DROP_FOREIGN_KEY)
 		    || ctx->num_to_drop_fk > 0);
 	DBUG_ASSERT(ctx->num_to_drop_fk
-		    == ha_alter_info->alter_info->drop_list.elements);
+		    <= ha_alter_info->alter_info->drop_list.elements);
 
 	for (dict_index_t* index = dict_table_get_first_index(rebuilt_table);
 	     index;
@@ -5309,7 +5317,7 @@ commit_try_norebuild(
 		      & Alter_inplace_info::DROP_FOREIGN_KEY)
 		    || ctx->num_to_drop_fk > 0);
 	DBUG_ASSERT(ctx->num_to_drop_fk
-		    == ha_alter_info->alter_info->drop_list.elements);
+		    <= ha_alter_info->alter_info->drop_list.elements);
 
 	for (ulint i = 0; i < ctx->num_to_add_index; i++) {
 		dict_index_t*	index = ctx->add_index[i];

storage/xtradb/handler/handler0alter.cc

@@ -3704,12 +3704,14 @@ ha_innobase::prepare_inplace_alter_table(
 				continue;
 			}
 
+			dict_foreign_t* foreign;
+
 			for (dict_foreign_set::iterator it
 				= prebuilt->table->foreign_set.begin();
 			     it != prebuilt->table->foreign_set.end();
 			     ++it) {
 
-				dict_foreign_t*	foreign = *it;
+				foreign = *it;
 				const char* fid = strchr(foreign->id, '/');
 
 				DBUG_ASSERT(fid);
@@ -3720,7 +3722,6 @@ ha_innobase::prepare_inplace_alter_table(
 
 				if (!my_strcasecmp(system_charset_info,
 						   fid, drop->name)) {
-					drop_fk[n_drop_fk++] = foreign;
 					goto found_fk;
 				}
 			}
@@ -3729,12 +3730,19 @@ ha_innobase::prepare_inplace_alter_table(
 				 drop->name);
 			goto err_exit;
 found_fk:
+			for (ulint i = n_drop_fk; i--; ) {
+				if (drop_fk[i] == foreign) {
+					goto dup_fk;
+				}
+			}
+			drop_fk[n_drop_fk++] = foreign;
+dup_fk:
 			continue;
 		}
 
 		DBUG_ASSERT(n_drop_fk > 0);
 		DBUG_ASSERT(n_drop_fk
-			    == ha_alter_info->alter_info->drop_list.elements);
+			    <= ha_alter_info->alter_info->drop_list.elements);
 	} else {
 		drop_fk = NULL;
 	}
@@ -5071,7 +5079,7 @@ commit_try_rebuild(
 		      & Alter_inplace_info::DROP_FOREIGN_KEY)
 		    || ctx->num_to_drop_fk > 0);
 	DBUG_ASSERT(ctx->num_to_drop_fk
-		    == ha_alter_info->alter_info->drop_list.elements);
+		    <= ha_alter_info->alter_info->drop_list.elements);
 
 	for (dict_index_t* index = dict_table_get_first_index(rebuilt_table);
 	     index;
@@ -5325,7 +5333,7 @@ commit_try_norebuild(
 		      & Alter_inplace_info::DROP_FOREIGN_KEY)
 		    || ctx->num_to_drop_fk > 0);
 	DBUG_ASSERT(ctx->num_to_drop_fk
-		    == ha_alter_info->alter_info->drop_list.elements);
+		    <= ha_alter_info->alter_info->drop_list.elements);
 
 	for (ulint i = 0; i < ctx->num_to_add_index; i++) {
 		dict_index_t*	index = ctx->add_index[i];