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

In the attachement you will find the source of a database extension that
I used to test this.

Extension test_spi_in_preload_session just executes 'select 1' in its
_PG_init() function.
Until Postgres version 14beta1 this works fine, but in version 14beta2
the process dies.

To compile:
make
make install

In postgresql.conf set:

log_min_messages = debug3
session_preload_libraries = 'test_spi_in_preload_session'

To test:
Just try to login to Postgres or execute
make installcheck

Regards,
Martin.

On 02/07/2021 09:10, PG Bug reporting form wrote:
> 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
>
--
Martin Butter
Developer

Splendid Data Nederland B.V.
Binnenhof 62A
1412 LC  NAARDEN

T: +31 (0)85 773 19 99
M: +31 (0)6 226 946 62
E: martin(dot)butter(at)splendiddata(dot)com <mailto:martin(dot)butter(at)splendiddata(dot)com>

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