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Commit31ed3cf

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Process session_preload_libraries within InitPostgres's transaction.
Previously we did this after InitPostgres, at a somewhat randomly chosenplace within PostgresMain. However, since commita0ffa88 doing thisoutside a transaction can cause a crash, if we need to check permissionswhile replacing a placeholder GUC. (Besides which, a preloaded librarycould itself want to do database access within _PG_init.)To avoid needing an additional transaction start/end in every session,move the process_session_preload_libraries call to within InitPostgres'stransaction. That requires teaching the code not to call it whenInitPostgres is called from somewhere other than PostgresMain, sincewe don't want session_preload_libraries to affect background workers.The most future-proof solution here seems to be to add an additionalflag parameter to InitPostgres; fortunately, we're not yet very worriedabout API stability for v15.Doing this also exposed the fact that we're currently honoringsession_preload_libraries in walsenders, even those not connected toany database. This seems, at minimum, a POLA violation: walsendersare not interactive sessions. Let's stop doing that.(All these comments also apply to local_preload_libraries, of course.)Per report from Gurjeet Singh (thanks also to Nathan Bossart and KyotaroHoriguchi for review). Backpatch to v15 wherea0ffa88 came in.Discussion:https://postgr.es/m/CABwTF4VEpwTHhRQ+q5MiC5ucngN-whN-PdcKeufX7eLSoAfbZA@mail.gmail.com
1 parent19f8232 commit31ed3cf

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6 files changed

+64
-25
lines changed

6 files changed

+64
-25
lines changed

‎src/backend/bootstrap/bootstrap.c‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -355,7 +355,7 @@ BootstrapModeMain(int argc, char *argv[], bool check_only)
355355
if (pg_link_canary_is_frontend())
356356
elog(ERROR,"backend is incorrectly linked to frontend functions");
357357

358-
InitPostgres(NULL,InvalidOid,NULL,InvalidOid,NULL, false);
358+
InitPostgres(NULL,InvalidOid,NULL,InvalidOid,false, false,NULL);
359359

360360
/* Initialize stuff for bootstrap-file processing */
361361
for (i=0;i<MAXATTR;i++)

‎src/backend/postmaster/autovacuum.c‎

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -475,7 +475,7 @@ AutoVacLauncherMain(int argc, char *argv[])
475475
/* Early initialization */
476476
BaseInit();
477477

478-
InitPostgres(NULL,InvalidOid,NULL,InvalidOid,NULL, false);
478+
InitPostgres(NULL,InvalidOid,NULL,InvalidOid,false, false,NULL);
479479

480480
SetProcessingMode(NormalProcessing);
481481

@@ -1694,12 +1694,13 @@ AutoVacWorkerMain(int argc, char *argv[])
16941694
pgstat_report_autovac(dbid);
16951695

16961696
/*
1697-
* Connect to the selected database
1697+
* Connect to the selected database, specifying no particular user
16981698
*
16991699
* Note: if we have selected a just-deleted database (due to using
17001700
* stale stats info), we'll fail and exit here.
17011701
*/
1702-
InitPostgres(NULL,dbid,NULL,InvalidOid,dbname, false);
1702+
InitPostgres(NULL,dbid,NULL,InvalidOid, false, false,
1703+
dbname);
17031704
SetProcessingMode(NormalProcessing);
17041705
set_ps_display(dbname);
17051706
ereport(DEBUG1,

‎src/backend/postmaster/postmaster.c‎

Lines changed: 10 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -5668,7 +5668,11 @@ BackgroundWorkerInitializeConnection(const char *dbname, const char *username, u
56685668
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
56695669
errmsg("database connection requirement not indicated during registration")));
56705670

5671-
InitPostgres(dbname,InvalidOid,username,InvalidOid,NULL, (flags&BGWORKER_BYPASS_ALLOWCONN)!=0);
5671+
InitPostgres(dbname,InvalidOid,/* database to connect to */
5672+
username,InvalidOid,/* role to connect as */
5673+
false,/* never honor session_preload_libraries */
5674+
(flags&BGWORKER_BYPASS_ALLOWCONN)!=0,/* ignore datallowconn? */
5675+
NULL);/* no out_dbname */
56725676

56735677
/* it had better not gotten out of "init" mode yet */
56745678
if (!IsInitProcessingMode())
@@ -5691,7 +5695,11 @@ BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, uint32 flags)
56915695
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
56925696
errmsg("database connection requirement not indicated during registration")));
56935697

5694-
InitPostgres(NULL,dboid,NULL,useroid,NULL, (flags&BGWORKER_BYPASS_ALLOWCONN)!=0);
5698+
InitPostgres(NULL,dboid,/* database to connect to */
5699+
NULL,useroid,/* role to connect as */
5700+
false,/* never honor session_preload_libraries */
5701+
(flags&BGWORKER_BYPASS_ALLOWCONN)!=0,/* ignore datallowconn? */
5702+
NULL);/* no out_dbname */
56955703

56965704
/* it had better not gotten out of "init" mode yet */
56975705
if (!IsInitProcessingMode())

‎src/backend/tcop/postgres.c‎

Lines changed: 5 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -4152,7 +4152,11 @@ PostgresMain(const char *dbname, const char *username)
41524152
* it inside InitPostgres() instead. In particular, anything that
41534153
* involves database access should be there, not here.
41544154
*/
4155-
InitPostgres(dbname,InvalidOid,username,InvalidOid,NULL, false);
4155+
InitPostgres(dbname,InvalidOid,/* database to connect to */
4156+
username,InvalidOid,/* role to connect as */
4157+
!am_walsender,/* honor session_preload_libraries? */
4158+
false,/* don't ignore datallowconn */
4159+
NULL);/* no out_dbname */
41564160

41574161
/*
41584162
* If the PostmasterContext is still around, recycle the space; we don't
@@ -4188,12 +4192,6 @@ PostgresMain(const char *dbname, const char *username)
41884192
if (am_walsender)
41894193
InitWalSender();
41904194

4191-
/*
4192-
* process any libraries that should be preloaded at backend start (this
4193-
* likewise can't be done until GUC settings are complete)
4194-
*/
4195-
process_session_preload_libraries();
4196-
41974195
/*
41984196
* Send this backend's cancellation info to the frontend.
41994197
*/

‎src/backend/utils/init/postinit.c‎

Lines changed: 39 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -622,29 +622,48 @@ BaseInit(void)
622622
* InitPostgres
623623
*Initialize POSTGRES.
624624
*
625+
* Parameters:
626+
*in_dbname, dboid: specify database to connect to, as described below
627+
*username, useroid: specify role to connect as, as described below
628+
*load_session_libraries: TRUE to honor [session|local]_preload_libraries
629+
*override_allow_connections: TRUE to connect despite !datallowconn
630+
*out_dbname: optional output parameter, see below; pass NULL if not used
631+
*
625632
* The database can be specified by name, using the in_dbname parameter, or by
626-
* OID, using the dboid parameter. In the latter case, the actual database
633+
* OID, using the dboid parameter. Specify NULL or InvalidOid respectively
634+
* for the unused parameter. If dboid is provided, the actual database
627635
* name can be returned to the caller in out_dbname. If out_dbname isn't
628636
* NULL, it must point to a buffer of size NAMEDATALEN.
629637
*
630-
* Similarly, theusername can be passed by name, using the username parameter,
638+
* Similarly, therole can be passed by name, using the username parameter,
631639
* or by OID using the useroid parameter.
632640
*
633-
* In bootstrap mode no parameters are used. The autovacuum launcher process
634-
* doesn't use any parameters either, because it only goes far enough to be
635-
* able to read pg_database; it doesn't connect to any particular database.
636-
* In walsender mode only username is used.
641+
* In bootstrap mode the database and username parameters are NULL/InvalidOid.
642+
* The autovacuum launcher process doesn't specify these parameters either,
643+
* because it only goes far enough to be able to read pg_database; it doesn't
644+
* connect to any particular database. An autovacuum worker specifies a
645+
* database but not a username; conversely, a physical walsender specifies
646+
* username but not database.
647+
*
648+
* By convention, load_session_libraries should be passed as true in
649+
* "interactive" sessions (including standalone backends), but false in
650+
* background processes such as autovacuum. Note in particular that it
651+
* shouldn't be true in parallel worker processes; those have another
652+
* mechanism for replicating their leader's set of loaded libraries.
637653
*
638-
*As of PostgreSQL 8.2, weexpect InitProcess() was already called, so we
639-
*already have aPGPROC struct ... but it's not completely filled in yet.
654+
*WeexpectthatInitProcess() was already called, so we already have a
655+
* PGPROC struct ... but it's not completely filled in yet.
640656
*
641657
* Note:
642658
*Be very careful with the order of calls in the InitPostgres function.
643659
* --------------------------------
644660
*/
645661
void
646-
InitPostgres(constchar*in_dbname,Oiddboid,constchar*username,
647-
Oiduseroid,char*out_dbname,booloverride_allow_connections)
662+
InitPostgres(constchar*in_dbname,Oiddboid,
663+
constchar*username,Oiduseroid,
664+
boolload_session_libraries,
665+
booloverride_allow_connections,
666+
char*out_dbname)
648667
{
649668
boolbootstrap=IsBootstrapProcessingMode();
650669
boolam_superuser;
@@ -1108,6 +1127,16 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
11081127
/* Initialize this backend's session state. */
11091128
InitializeSession();
11101129

1130+
/*
1131+
* If this is an interactive session, load any libraries that should be
1132+
* preloaded at backend start. Since those are determined by GUCs, this
1133+
* can't happen until GUC settings are complete, but we want it to happen
1134+
* during the initial transaction in case anything that requires database
1135+
* access needs to be done.
1136+
*/
1137+
if (load_session_libraries)
1138+
process_session_preload_libraries();
1139+
11111140
/* report this backend in the PgBackendStatus array */
11121141
if (!bootstrap)
11131142
pgstat_bestart();

‎src/include/miscadmin.h‎

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -457,8 +457,11 @@ extern PGDLLIMPORT AuxProcType MyAuxProcType;
457457
/* in utils/init/postinit.c */
458458
externvoidpg_split_opts(char**argv,int*argcp,constchar*optstr);
459459
externvoidInitializeMaxBackends(void);
460-
externvoidInitPostgres(constchar*in_dbname,Oiddboid,constchar*username,
461-
Oiduseroid,char*out_dbname,booloverride_allow_connections);
460+
externvoidInitPostgres(constchar*in_dbname,Oiddboid,
461+
constchar*username,Oiduseroid,
462+
boolload_session_libraries,
463+
booloverride_allow_connections,
464+
char*out_dbname);
462465
externvoidBaseInit(void);
463466

464467
/* in utils/init/miscinit.c */

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