BUG #17081: Segmentation fault on _PG_init() in a session_preload_library

The following bug has been logged on the website:

Bug reference: 17081
Logged by: Martin Butter
Email address: martin(dot)butter(at)splendiddata(dot)com
PostgreSQL version: 14beta2
Operating system: Fedora 33
Description:

Code used:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

#include "postgres.h"
#include "executor/spi.h"
#include "miscadmin.h"
#include "commands/dbcommands.h"
#include "access/xact.h"

#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif

void _PG_init(void);
/* Module entry point */
void _PG_init(void)
{
char* dbName;
int startedATransaction = 0;
int spiStatus;
ErrorData *edata;

elog(DEBUG3,
"_PG_init() in test_spi_in_preload_session.so, MyProcPid=%d,
MyDatabaseId=%d, IsBackgroundWorker=%d",
MyProcPid, MyDatabaseId, IsBackgroundWorker);

/*
* If no database is selected, don't execute the code
* This may occur for example in a replication target database.
*/
if (!OidIsValid(MyDatabaseId)) {
elog(DEBUG1, "No database selected so test_spi_in_preload_session will
not execute");
return;
}

/*
* Don't try to execute in a parallel worker
*/
if (IsBackgroundWorker)
{
elog(DEBUG1,
"test_spi_in_preload_session did not do anything because we are in a
background worker");
return;
}

if (GetCurrentTransactionIdIfAny() == InvalidTransactionId)
{
/*
* If we're not in a transaction, start one.
*/
StartTransactionCommand();
startedATransaction = 1;
}

dbName = get_database_name(MyDatabaseId);
Assert(dbName); // warning: only active if kernel compiled with
--enable-cassert

spiStatus = SPI_connect();
if (spiStatus != SPI_OK_CONNECT) {
ereport(ERROR,
( errmsg("SPI_connect returned %d for database %s",
spiStatus,
dbName)));
}

// if ones gets error in SPI_execute(), the function does not
return, unless protected by a PG_TRY / PG_CATCH
PG_TRY();
{
elog(DEBUG3,
"test_spi_in_preload_session will execute 'select
1' in database %s",
dbName);
spiStatus = SPI_execute("select 1", false, 1);
if (spiStatus < 0) {
ereport(ERROR,
( errmsg("SPI_execute returned %d for query 'select
1' in database %s",
spiStatus,
dbName)));
}
elog(DEBUG3,
"test_spi_in_preload_session is back from 'select 1' in
database %s",
dbName);
}
PG_CATCH();
{
AbortCurrentTransaction();
edata = CopyErrorData();
ereport(WARNING,
( errcode(edata->sqlerrcode),
errmsg("test_spi_in_preload_session failed to execute
'select 1' in database %s",
dbName),
errhint("original message = %s", edata->message)));
}
PG_END_TRY();

SPI_finish();

if (startedATransaction)
{
/*
* commit the transaction we started
*/
CommitTransactionCommand();
}
}
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Serverlog:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
.
.
2021-07-02 08:43:43.295 CEST [37478] LOG: database system is ready to
accept connections
2021-07-02 08:43:43.295 CEST [37487] DEBUG: InitPostgres
2021-07-02 08:43:43.295 CEST [37488] DEBUG: removing permanent stats file
"pg_stat/global.stat"
2021-07-02 08:43:43.296 CEST [37489] DEBUG: logical replication launcher
started
2021-07-02 08:43:43.296 CEST [37489] DEBUG: InitPostgres
2021-07-02 08:43:43.300 CEST [37488] DEBUG: received inquiry for database
0
2021-07-02 08:43:43.300 CEST [37488] DEBUG: writing stats file
"pg_stat_tmp/global.stat"
2021-07-02 08:43:51.664 CEST [37478] DEBUG: forked new backend, pid=37558
socket=9
2021-07-02 08:43:51.665 CEST [37558] DEBUG: InitPostgres
2021-07-02 08:43:51.677 CEST [37558] DEBUG: find_in_dynamic_libpath: trying
"/usr/local/postgresql-14beta2/lib/test_spi_in_preload_session"
2021-07-02 08:43:51.677 CEST [37558] DEBUG: find_in_dynamic_libpath: trying
"/usr/local/postgresql-14beta2/lib/test_spi_in_preload_session.so"
2021-07-02 08:43:51.677 CEST [37558] DEBUG: _PG_init() in
test_spi_in_preload_session.so, MyProcPid=37558, MyDatabaseId=13977,
IsBackgroundWorker=0
2021-07-02 08:43:51.677 CEST [37558] DEBUG: test_spi_in_preload_session
will execute 'select 1' in database postgres
2021-07-02 08:43:51.984 CEST [37478] DEBUG: server process (PID 37558) was
terminated by signal 11: Segmentation fault
2021-07-02 08:43:51.984 CEST [37478] LOG: server process (PID 37558) was
terminated by signal 11: Segmentation fault
2021-07-02 08:43:51.984 CEST [37478] LOG: terminating any other active
server processes
2021-07-02 08:43:51.984 CEST [37478] DEBUG: sending SIGQUIT to process
37489
2021-07-02 08:43:51.984 CEST [37478] DEBUG: sending SIGQUIT to process
37485
2021-07-02 08:43:51.984 CEST [37478] DEBUG: sending SIGQUIT to process
37484
2021-07-02 08:43:51.984 CEST [37478] DEBUG: sending SIGQUIT to process
37486
2021-07-02 08:43:51.984 CEST [37478] DEBUG: sending SIGQUIT to process
37487
2021-07-02 08:43:51.984 CEST [37478] DEBUG: sending SIGQUIT to process
37488
2021-07-02 08:43:51.984 CEST [37488] DEBUG: writing stats file
"pg_stat/global.stat"
2021-07-02 08:43:51.984 CEST [37488] DEBUG: shmem_exit(-1): 0
before_shmem_exit callbacks to make
2021-07-02 08:43:51.984 CEST [37488] DEBUG: shmem_exit(-1): 0 on_shmem_exit
callbacks to make
2021-07-02 08:43:51.984 CEST [37488] DEBUG: proc_exit(-1): 0 callbacks to
make
2021-07-02 08:43:51.985 CEST [37478] LOG: all server processes terminated;
reinitializing
2021-07-02 08:43:51.985 CEST [37478] DEBUG: shmem_exit(1): 0
before_shmem_exit callbacks to make
2021-07-02 08:43:51.985 CEST [37478] DEBUG: shmem_exit(1): 5 on_shmem_exit
callbacks to make
2021-07-02 08:43:51.985 CEST [37478] DEBUG: cleaning up dynamic shared
memory control segment with ID 2085192430
2021-07-02 08:43:51.997 CEST [37478] DEBUG: invoking
IpcMemoryCreate(size=148856832)
2021-07-02 08:43:51.997 CEST [37478] DEBUG: mmap(148897792) with
MAP_HUGETLB failed, huge pages disabled: Cannot allocate memory
2021-07-02 08:43:52.005 CEST [37478] DEBUG: dynamic shared memory system
will support 674 segments
2021-07-02 08:43:52.005 CEST [37478] DEBUG: created dynamic shared memory
control segment 289087702 (26976 bytes)
2021-07-02 08:43:52.006 CEST [37574] LOG: database system was interrupted;
last known up at 2021-07-02 08:43:43 CEST
2021-07-02 08:43:52.006 CEST [37574] DEBUG: removing all temporary WAL
segments
2021-07-02 08:43:52.174 CEST [37574] DEBUG: checkpoint record is at
0/439D020
2021-07-02 08:43:52.174 CEST [37574] DEBUG: redo record is at 0/439D020;
shutdown true
2021-07-02 08:43:52.174 CEST [37574] DEBUG: next transaction ID: 19078;
next OID: 111557
2021-07-02 08:43:52.174 CEST [37574] DEBUG: next MultiXactId: 1; next
MultiXactOffset: 0
2021-07-02 08:43:52.174 CEST [37574] DEBUG: oldest unfrozen transaction ID:
726, in database 1
2021-07-02 08:43:52.174 CEST [37574] DEBUG: oldest MultiXactId: 1, in
database 1
2021-07-02 08:43:52.174 CEST [37574] DEBUG: commit timestamp Xid
oldest/newest: 0/0
2021-07-02 08:43:52.174 CEST [37574] DEBUG: transaction ID wrap limit is
2147484373, limited by database with OID 1
2021-07-02 08:43:52.174 CEST [37574] DEBUG: MultiXactId wrap limit is
2147483648, limited by database with OID 1
2021-07-02 08:43:52.174 CEST [37574] DEBUG: starting up replication slots
2021-07-02 08:43:52.174 CEST [37574] DEBUG: starting up replication origin
progress state
2021-07-02 08:43:52.174 CEST [37574] LOG: database system was not properly
shut down; automatic recovery in progress
2021-07-02 08:43:52.176 CEST [37574] DEBUG: resetting unlogged relations:
cleanup 1 init 0
2021-07-02 08:43:52.176 CEST [37574] LOG: invalid record length at
0/439D098: wanted 24, got 0
2021-07-02 08:43:52.176 CEST [37574] LOG: redo is not required
2021-07-02 08:43:52.176 CEST [37574] DEBUG: resetting unlogged relations:
cleanup 0 init 1
2021-07-02 08:43:52.180 CEST [37574] DEBUG: performing replication slot
checkpoint
2021-07-02 08:43:52.186 CEST [37574] DEBUG: attempting to remove WAL
segments older than log file 000000000000000000000003
2021-07-02 08:43:52.186 CEST [37574] DEBUG: MultiXactId wrap limit is
2147483648, limited by database with OID 1
2021-07-02 08:43:52.186 CEST [37574] DEBUG: MultiXact member stop limit is
now 4294914944 based on MultiXact 1
2021-07-02 08:43:52.187 CEST [37574] DEBUG: shmem_exit(0): 1
before_shmem_exit callbacks to make
2021-07-02 08:43:52.187 CEST [37574] DEBUG: shmem_exit(0): 7 on_shmem_exit
callbacks to make
2021-07-02 08:43:52.187 CEST [37574] DEBUG: proc_exit(0): 2 callbacks to
make
2021-07-02 08:43:52.187 CEST [37574] DEBUG: exit(0)
2021-07-02 08:43:52.187 CEST [37574] DEBUG: shmem_exit(-1): 0
before_shmem_exit callbacks to make
2021-07-02 08:43:52.187 CEST [37574] DEBUG: shmem_exit(-1): 0 on_shmem_exit
callbacks to make
2021-07-02 08:43:52.187 CEST [37574] DEBUG: proc_exit(-1): 0 callbacks to
make
2021-07-02 08:43:52.188 CEST [37575] DEBUG: checkpointer updated shared
memory configuration values
2021-07-02 08:43:52.188 CEST [37478] DEBUG: starting background worker
process "logical replication launcher"
2021-07-02 08:43:52.189 CEST [37578] DEBUG: autovacuum launcher started
2021-07-02 08:43:52.189 CEST [37478] LOG: database system is ready to
accept connections
2021-07-02 08:43:52.189 CEST [37578] DEBUG: InitPostgres
2021-07-02 08:43:52.189 CEST [37580] DEBUG: logical replication launcher
started
2021-07-02 08:43:52.189 CEST [37580] DEBUG: InitPostgres
2021-07-02 08:43:52.189 CEST [37579] DEBUG: received inquiry for database
0
2021-07-02 08:43:52.189 CEST [37579] DEBUG: writing stats file
"pg_stat_tmp/global.stat"
2021-07-02 08:44:07.209 CEST [37576] DEBUG: snapshot of 0+0 running
transaction ids (lsn 0/439D148 oldest xid 19078 latest complete 19077 next
xid 19078)
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Remarks:
Until version 14beta1 this worked fine, but in version 14beta2 the
SPI_execute() call fails