Hi,
On Tue, Apr 23, 2024 at 04:59:09AM +0000, Bertrand Drouvot wrote:
> Hi,
>
> On Mon, Apr 22, 2024 at 03:00:00PM +0300, Alexander Lakhin wrote:
> > 22.04.2024 13:52, Bertrand Drouvot wrote:
> > >
> > > That's weird, I just launched it several times with the patch applied and
> > > I'm not
> > > able to see the seg fault (while I can see it constently failing on the
> > > master
> > > branch).
> > >
> > > Are you 100% sure you tested it against a binary with the patch applied?
> > >
> >
> > Yes, at least I can't see what I'm doing wrong. Please try my
> > self-contained script attached.
>
> Thanks for sharing your script!
>
> Yeah your script ensures the patch is applied before the repro is executed.
>
> I do confirm that I can also see the issue with the patch applied (but I had
> to
> launch multiple attempts, while on master one attempt is enough).
>
> I'll have a look.
Please find attached v2 that should not produce the issue anymore (I launched a
lot of attempts without any issues). v1 was not strong enough as it was not
always checking for the dependent object existence. v2 now always checks if the
object still exists after the additional lock acquisition attempt while
recording
the dependency.
I still need to think about v2 but in the meantime could you please also give
v2 a try on you side?
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
>From f80fdfc32e791463555aa318f26ff5e7363ac3ac Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot...@gmail.com>
Date: Fri, 29 Mar 2024 15:43:26 +0000
Subject: [PATCH v2] Avoid orphaned objects dependencies
It's currently possible to create orphaned objects dependencies, for example:
Scenario 1:
session 1: begin; drop schema schem;
session 2: create a function in the schema schem
session 1: commit;
With the above, the function created in session 2 would be linked to a non
existing schema.
Scenario 2:
session 1: begin; create a function in the schema schem
session 2: drop schema schem;
session 1: commit;
With the above, the function created in session 1 would be linked to a non
existing schema.
To avoid those scenarios, a new lock (that conflicts with a lock taken by DROP)
has been put in place when the dependencies are being recorded. With this in
place, the drop schema in scenario 2 would be locked.
Also, after locking the object, the patch checks that the object still exists:
with this in place session 2 in scenario 1 would be locked and would report an
error once session 1 committs (that would not be the case should session 1 abort
the transaction).
The patch adds a few tests for some dependency cases (that would currently produce
orphaned objects):
- schema and function (as the above scenarios)
- function and type
- table and type
---
src/backend/catalog/dependency.c | 48 +++++++++++++
src/backend/catalog/objectaddress.c | 70 +++++++++++++++++++
src/backend/catalog/pg_depend.c | 6 ++
src/include/catalog/dependency.h | 1 +
src/include/catalog/objectaddress.h | 1 +
src/test/modules/Makefile | 1 +
src/test/modules/meson.build | 1 +
.../test_dependencies_locks/.gitignore | 3 +
.../modules/test_dependencies_locks/Makefile | 14 ++++
.../expected/test_dependencies_locks.out | 49 +++++++++++++
.../test_dependencies_locks/meson.build | 12 ++++
.../specs/test_dependencies_locks.spec | 39 +++++++++++
12 files changed, 245 insertions(+)
38.1% src/backend/catalog/
30.7% src/test/modules/test_dependencies_locks/expected/
19.5% src/test/modules/test_dependencies_locks/specs/
8.7% src/test/modules/test_dependencies_locks/
diff --git a/src/backend/catalog/dependency.c b/src/backend/catalog/dependency.c
index d4b5b2ade1..e3b66025dd 100644
--- a/src/backend/catalog/dependency.c
+++ b/src/backend/catalog/dependency.c
@@ -1517,6 +1517,54 @@ AcquireDeletionLock(const ObjectAddress *object, int flags)
}
}
+/*
+ * depLockAndCheckObject
+ *
+ * Lock the object that we are about to record a dependency on.
+ * After it's locked, verify that it hasn't been dropped while we
+ * weren't looking. If the object has been dropped, this function
+ * does not return!
+ */
+void
+depLockAndCheckObject(const ObjectAddress *object)
+{
+ char *object_description;
+
+ /*
+ * Those don't rely on LockDatabaseObject() when being dropped (see
+ * AcquireDeletionLock()). Also it looks like they can not produce
+ * orphaned dependent objects when being dropped.
+ */
+ if (object->classId == RelationRelationId || object->classId == AuthMemRelationId)
+ return;
+
+ object_description = getObjectDescription(object, true);
+
+ /* assume we should lock the whole object not a sub-object */
+ LockDatabaseObject(object->classId, object->objectId, 0, AccessShareLock);
+
+ /* check if object still exists */
+ if (!ObjectByIdExist(object, false))
+ {
+ /*
+ * It might be possible that we are creating it, so bypass the syscache
+ * lookup and use a dirty snaphot instead.
+ */
+ if (!ObjectByIdExist(object, true))
+ {
+ if(object_description)
+ ereport(ERROR, errmsg("%s does not exist", object_description));
+ else
+ ereport(ERROR, errmsg("a dependent object does not exist"));
+ }
+ }
+
+ if (object_description)
+ pfree(object_description);
+
+ return;
+}
+
/*
* ReleaseDeletionLock - release an object deletion lock
*
diff --git a/src/backend/catalog/objectaddress.c b/src/backend/catalog/objectaddress.c
index 7b536ac6fd..c2b873dd81 100644
--- a/src/backend/catalog/objectaddress.c
+++ b/src/backend/catalog/objectaddress.c
@@ -2590,6 +2590,76 @@ get_object_namespace(const ObjectAddress *address)
return oid;
}
+/*
+ * ObjectByIdExist
+ *
+ * Return whether the given object exists.
+ *
+ * Works for most catalogs, if no special processing is needed.
+ */
+bool
+ObjectByIdExist(const ObjectAddress *address, bool use_dirty_snapshot)
+{
+ HeapTuple tuple;
+ int cache = -1;
+ const ObjectPropertyType *property;
+
+ if (!use_dirty_snapshot)
+ {
+ property = get_object_property_data(address->classId);
+
+ cache = property->oid_catcache_id;
+ }
+
+ if (cache >= 0)
+ {
+ /* Fetch tuple from syscache. */
+ tuple = SearchSysCache1(cache, ObjectIdGetDatum(address->objectId));
+
+ if (!HeapTupleIsValid(tuple))
+ {
+ return false;
+ }
+
+ ReleaseSysCache(tuple);
+
+ return true;
+ }
+ else
+ {
+ Relation rel;
+ ScanKeyData skey[1];
+ SysScanDesc scan;
+ SnapshotData DirtySnapshot;
+ Snapshot snapshot;
+
+ if (use_dirty_snapshot)
+ {
+ InitDirtySnapshot(DirtySnapshot);
+ snapshot = &DirtySnapshot;
+ }
+ else
+ snapshot = NULL;
+
+ rel = table_open(address->classId, AccessShareLock);
+
+ ScanKeyInit(&skey[0],
+ get_object_attnum_oid(address->classId),
+ BTEqualStrategyNumber, F_OIDEQ,
+ ObjectIdGetDatum(address->objectId));
+
+ scan = systable_beginscan(rel, get_object_oid_index(address->classId), true,
+ snapshot, 1, skey);
+
+ /* we expect exactly one match */
+ tuple = systable_getnext(scan);
+ systable_endscan(scan);
+ table_close(rel, AccessShareLock);
+
+ return (HeapTupleIsValid(tuple));
+ }
+}
+
/*
* Return ObjectType for the given object type as given by
* getObjectTypeDescription; if no valid ObjectType code exists, but it's a
diff --git a/src/backend/catalog/pg_depend.c b/src/backend/catalog/pg_depend.c
index f85a898de8..6bb218f5dd 100644
--- a/src/backend/catalog/pg_depend.c
+++ b/src/backend/catalog/pg_depend.c
@@ -106,6 +106,12 @@ recordMultipleDependencies(const ObjectAddress *depender,
if (isObjectPinned(referenced))
continue;
+ /*
+ * Acquire a lock and check object still exists while recording the
+ * dependency. XXX - Should we do so only for DEPENDENCY_NORMAL?
+ */
+ depLockAndCheckObject(referenced);
+
if (slot_init_count < max_slots)
{
slot[slot_stored_count] = MakeSingleTupleTableSlot(RelationGetDescr(dependDesc),
diff --git a/src/include/catalog/dependency.h b/src/include/catalog/dependency.h
index ec654010d4..8915548711 100644
--- a/src/include/catalog/dependency.h
+++ b/src/include/catalog/dependency.h
@@ -94,6 +94,7 @@ typedef struct ObjectAddresses ObjectAddresses;
/* in dependency.c */
extern void AcquireDeletionLock(const ObjectAddress *object, int flags);
+extern void depLockAndCheckObject(const ObjectAddress *object);
extern void ReleaseDeletionLock(const ObjectAddress *object);
diff --git a/src/include/catalog/objectaddress.h b/src/include/catalog/objectaddress.h
index 3a70d80e32..04891abcc1 100644
--- a/src/include/catalog/objectaddress.h
+++ b/src/include/catalog/objectaddress.h
@@ -53,6 +53,7 @@ extern void check_object_ownership(Oid roleid,
Node *object, Relation relation);
extern Oid get_object_namespace(const ObjectAddress *address);
+extern bool ObjectByIdExist(const ObjectAddress *address, bool use_dirty_snapshot);
extern bool is_objectclass_supported(Oid class_id);
extern const char *get_object_class_descr(Oid class_id);
diff --git a/src/test/modules/Makefile b/src/test/modules/Makefile
index 256799f520..75f357100f 100644
--- a/src/test/modules/Makefile
+++ b/src/test/modules/Makefile
@@ -17,6 +17,7 @@ SUBDIRS = \
test_copy_callbacks \
test_custom_rmgrs \
test_ddl_deparse \
+ test_dependencies_locks \
test_dsa \
test_dsm_registry \
test_extensions \
diff --git a/src/test/modules/meson.build b/src/test/modules/meson.build
index d8fe059d23..60305dcccd 100644
--- a/src/test/modules/meson.build
+++ b/src/test/modules/meson.build
@@ -16,6 +16,7 @@ subdir('test_bloomfilter')
subdir('test_copy_callbacks')
subdir('test_custom_rmgrs')
subdir('test_ddl_deparse')
+subdir('test_dependencies_locks')
subdir('test_dsa')
subdir('test_dsm_registry')
subdir('test_extensions')
diff --git a/src/test/modules/test_dependencies_locks/.gitignore b/src/test/modules/test_dependencies_locks/.gitignore
new file mode 100644
index 0000000000..bf000faac4
--- /dev/null
+++ b/src/test/modules/test_dependencies_locks/.gitignore
@@ -0,0 +1,3 @@
+# Generated subdirectories
+/log/
+/output_iso
diff --git a/src/test/modules/test_dependencies_locks/Makefile b/src/test/modules/test_dependencies_locks/Makefile
new file mode 100644
index 0000000000..7491048380
--- /dev/null
+++ b/src/test/modules/test_dependencies_locks/Makefile
@@ -0,0 +1,14 @@
+# src/test/modules/test_dependencies_locks/Makefile
+
+ISOLATION = test_dependencies_locks
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = src/test/modules/test_dependencies_locks
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
diff --git a/src/test/modules/test_dependencies_locks/expected/test_dependencies_locks.out b/src/test/modules/test_dependencies_locks/expected/test_dependencies_locks.out
new file mode 100644
index 0000000000..d0980f77d5
--- /dev/null
+++ b/src/test/modules/test_dependencies_locks/expected/test_dependencies_locks.out
@@ -0,0 +1,49 @@
+Parsed test spec with 2 sessions
+
+starting permutation: s1_begin s1_create_function_in_schema s2_drop_schema s1_commit
+step s1_begin: BEGIN;
+step s1_create_function_in_schema: CREATE FUNCTION testschema.foo() RETURNS int AS 'select 1' LANGUAGE sql;
+step s2_drop_schema: DROP SCHEMA testschema; <waiting ...>
+step s1_commit: COMMIT;
+step s2_drop_schema: <... completed>
+ERROR: cannot drop schema testschema because other objects depend on it
+
+starting permutation: s2_begin s2_drop_schema s1_create_function_in_schema s2_commit
+step s2_begin: BEGIN;
+step s2_drop_schema: DROP SCHEMA testschema;
+step s1_create_function_in_schema: CREATE FUNCTION testschema.foo() RETURNS int AS 'select 1' LANGUAGE sql; <waiting ...>
+step s2_commit: COMMIT;
+step s1_create_function_in_schema: <... completed>
+ERROR: schema testschema does not exist
+
+starting permutation: s1_begin s1_create_function_with_type s2_drop_foo_type s1_commit
+step s1_begin: BEGIN;
+step s1_create_function_with_type: CREATE FUNCTION footype(num foo) RETURNS int AS 'select 1' LANGUAGE sql;
+step s2_drop_foo_type: DROP TYPE public.foo; <waiting ...>
+step s1_commit: COMMIT;
+step s2_drop_foo_type: <... completed>
+ERROR: cannot drop type foo because other objects depend on it
+
+starting permutation: s2_begin s2_drop_foo_type s1_create_function_with_type s2_commit
+step s2_begin: BEGIN;
+step s2_drop_foo_type: DROP TYPE public.foo;
+step s1_create_function_with_type: CREATE FUNCTION footype(num foo) RETURNS int AS 'select 1' LANGUAGE sql; <waiting ...>
+step s2_commit: COMMIT;
+step s1_create_function_with_type: <... completed>
+ERROR: type foo does not exist
+
+starting permutation: s1_begin s1_create_table_with_type s2_drop_footab_type s1_commit
+step s1_begin: BEGIN;
+step s1_create_table_with_type: CREATE TABLE tabtype(a footab);
+step s2_drop_footab_type: DROP TYPE public.footab; <waiting ...>
+step s1_commit: COMMIT;
+step s2_drop_footab_type: <... completed>
+ERROR: cannot drop type footab because other objects depend on it
+
+starting permutation: s2_begin s2_drop_footab_type s1_create_table_with_type s2_commit
+step s2_begin: BEGIN;
+step s2_drop_footab_type: DROP TYPE public.footab;
+step s1_create_table_with_type: CREATE TABLE tabtype(a footab); <waiting ...>
+step s2_commit: COMMIT;
+step s1_create_table_with_type: <... completed>
+ERROR: type footab does not exist
diff --git a/src/test/modules/test_dependencies_locks/meson.build b/src/test/modules/test_dependencies_locks/meson.build
new file mode 100644
index 0000000000..92a978ab93
--- /dev/null
+++ b/src/test/modules/test_dependencies_locks/meson.build
@@ -0,0 +1,12 @@
+# Copyright (c) 2024, PostgreSQL Global Development Group
+
+tests += {
+ 'name': 'test_dependencies_locks',
+ 'sd': meson.current_source_dir(),
+ 'bd': meson.current_build_dir(),
+ 'isolation': {
+ 'specs': [
+ 'test_dependencies_locks',
+ ],
+ },
+}
diff --git a/src/test/modules/test_dependencies_locks/specs/test_dependencies_locks.spec b/src/test/modules/test_dependencies_locks/specs/test_dependencies_locks.spec
new file mode 100644
index 0000000000..fd15bd2a78
--- /dev/null
+++ b/src/test/modules/test_dependencies_locks/specs/test_dependencies_locks.spec
@@ -0,0 +1,39 @@
+setup
+{
+ CREATE SCHEMA testschema;
+ CREATE TYPE public.foo as enum ('one', 'two');
+ CREATE TYPE public.footab as enum ('three', 'four');
+}
+
+teardown
+{
+ DROP FUNCTION IF EXISTS testschema.foo();
+ DROP FUNCTION IF EXISTS footype(num foo);
+ DROP TABLE IF EXISTS tabtype;
+ DROP SCHEMA IF EXISTS testschema;
+ DROP TYPE IF EXISTS public.foo;
+ DROP TYPE IF EXISTS public.footab;
+}
+
+session "s1"
+
+step "s1_begin" { BEGIN; }
+step "s1_create_function_in_schema" { CREATE FUNCTION testschema.foo() RETURNS int AS 'select 1' LANGUAGE sql; }
+step "s1_create_function_with_type" { CREATE FUNCTION footype(num foo) RETURNS int AS 'select 1' LANGUAGE sql; }
+step "s1_create_table_with_type" { CREATE TABLE tabtype(a footab); }
+step "s1_commit" { COMMIT; }
+
+session "s2"
+
+step "s2_begin" { BEGIN; }
+step "s2_drop_schema" { DROP SCHEMA testschema; }
+step "s2_drop_foo_type" { DROP TYPE public.foo; }
+step "s2_drop_footab_type" { DROP TYPE public.footab; }
+step "s2_commit" { COMMIT; }
+
+permutation "s1_begin" "s1_create_function_in_schema" "s2_drop_schema" "s1_commit"
+permutation "s2_begin" "s2_drop_schema" "s1_create_function_in_schema" "s2_commit"
+permutation "s1_begin" "s1_create_function_with_type" "s2_drop_foo_type" "s1_commit"
+permutation "s2_begin" "s2_drop_foo_type" "s1_create_function_with_type" "s2_commit"
+permutation "s1_begin" "s1_create_table_with_type" "s2_drop_footab_type" "s1_commit"
+permutation "s2_begin" "s2_drop_footab_type" "s1_create_table_with_type" "s2_commit"
--
2.34.1
