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Commit2113ac4

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Don't use bgw_main even to specify in-core bgworker entrypoints.
On EXEC_BACKEND builds, this can fail if ASLR is in use.Backpatch to 9.5. On master, completely remove the bgw_main fieldcompletely, since there is no situation in which it is safe for anEXEC_BACKEND build. On 9.6 and 9.5, leave the field intact to avoidbreaking things for third-party code that doesn't care about workingunder EXEC_BACKEND. Prior to 9.5, there are no in-core bgworkerentrypoints.Petr Jelinek, reviewed by me.Discussion:http://postgr.es/m/09d8ad33-4287-a09b-a77f-77f8761adb5e@2ndquadrant.com
1 parentc281cd5 commit2113ac4

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8 files changed

+75
-66
lines changed

8 files changed

+75
-66
lines changed

‎doc/src/sgml/bgworker.sgml

Lines changed: 9 additions & 27 deletions
Original file line numberDiff line numberDiff line change
@@ -54,9 +54,8 @@ typedef struct BackgroundWorker
5454
int bgw_flags;
5555
BgWorkerStartTime bgw_start_time;
5656
int bgw_restart_time; /* in seconds, or BGW_NEVER_RESTART */
57-
bgworker_main_type bgw_main;
58-
char bgw_library_name[BGW_MAXLEN]; /* only if bgw_main is NULL */
59-
char bgw_function_name[BGW_MAXLEN]; /* only if bgw_main is NULL */
57+
char bgw_library_name[BGW_MAXLEN];
58+
char bgw_function_name[BGW_MAXLEN];
6059
Datum bgw_main_arg;
6160
char bgw_extra[BGW_EXTRALEN];
6261
int bgw_notify_pid;
@@ -130,27 +129,13 @@ typedef struct BackgroundWorker
130129
process in case of a crash.
131130
</para>
132131

133-
<para>
134-
<structfield>bgw_main</structfield> is a pointer to the function to run when
135-
the process is started. This field can only safely be used to launch
136-
functions within the core server, because shared libraries may be loaded
137-
at different starting addresses in different backend processes. This will
138-
happen on all platforms when the library is loaded using any mechanism
139-
other than <xref linkend="guc-shared-preload-libraries">. Even when that
140-
mechanism is used, address space layout variations will still occur on
141-
Windows, and when <literal>EXEC_BACKEND</> is used. Therefore, most users
142-
of this API should set this field to NULL. If it is non-NULL, it takes
143-
precedence over <structfield>bgw_library_name</> and
144-
<structfield>bgw_function_name</>.
145-
</para>
146-
147132
<para>
148133
<structfield>bgw_library_name</structfield> is the name of a library in
149134
which the initial entry point for the background worker should be sought.
150135
The named library will be dynamically loaded by the worker process and
151136
<structfield>bgw_function_name</structfield> will be used to identify the
152-
function to be called. If loading a function from the core code,
153-
<structfield>bgw_main</> shouldbe setinstead.
137+
function to be called. If loading a function from the core code, this must
138+
be setto "postgres".
154139
</para>
155140

156141
<para>
@@ -161,13 +146,10 @@ typedef struct BackgroundWorker
161146

162147
<para>
163148
<structfield>bgw_main_arg</structfield> is the <type>Datum</> argument
164-
to the background worker main function. Regardless of whether that
165-
function is specified via <structfield>bgw_main</> or via the combination
166-
of <function>bgw_library_name</> and <function>bgw_function_name</>,
167-
this main function should take a single argument of type <type>Datum</>
168-
and return <type>void</>. <structfield>bgw_main_arg</structfield> will be
169-
passed as the argument. In addition, the global variable
170-
<literal>MyBgworkerEntry</literal>
149+
to the background worker main function. This main function should take a
150+
single argument of type <type>Datum</> and return <type>void</>.
151+
<structfield>bgw_main_arg</structfield> will be passed as the argument.
152+
In addition, the global variable <literal>MyBgworkerEntry</literal>
171153
points to a copy of the <structname>BackgroundWorker</structname> structure
172154
passed at registration time; the worker may find it helpful to examine
173155
this structure.
@@ -215,7 +197,7 @@ typedef struct BackgroundWorker
215197

216198
<para>
217199
Signals are initially blocked when control reaches the
218-
<structfield>bgw_main</> function, and must be unblocked by it; this is to
200+
background worker's main function, and must be unblocked by it; this is to
219201
allow the process to customize its signal handlers, if necessary.
220202
Signals can be unblocked in the new process by calling
221203
<function>BackgroundWorkerUnblockSignals</> and blocked by calling

‎src/backend/access/transam/parallel.c

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -110,7 +110,6 @@ static dlist_head pcxt_list = DLIST_STATIC_INIT(pcxt_list);
110110
/* Private functions. */
111111
staticvoidHandleParallelMessage(ParallelContext*pcxt,inti,StringInfomsg);
112112
staticvoidParallelExtensionTrampoline(dsm_segment*seg,shm_toc*toc);
113-
staticvoidParallelWorkerMain(Datummain_arg);
114113
staticvoidWaitForParallelWorkersToExit(ParallelContext*pcxt);
115114

116115

@@ -458,7 +457,8 @@ LaunchParallelWorkers(ParallelContext *pcxt)
458457
|BGWORKER_CLASS_PARALLEL;
459458
worker.bgw_start_time=BgWorkerStart_ConsistentState;
460459
worker.bgw_restart_time=BGW_NEVER_RESTART;
461-
worker.bgw_main=ParallelWorkerMain;
460+
sprintf(worker.bgw_library_name,"postgres");
461+
sprintf(worker.bgw_function_name,"ParallelWorkerMain");
462462
worker.bgw_main_arg=UInt32GetDatum(dsm_segment_handle(pcxt->seg));
463463
worker.bgw_notify_pid=MyProcPid;
464464
memset(&worker.bgw_extra,0,BGW_EXTRALEN);
@@ -931,7 +931,7 @@ AtEOXact_Parallel(bool isCommit)
931931
/*
932932
* Main entrypoint for parallel workers.
933933
*/
934-
staticvoid
934+
void
935935
ParallelWorkerMain(Datummain_arg)
936936
{
937937
dsm_segment*seg;

‎src/backend/postmaster/bgworker.c

Lines changed: 53 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -15,12 +15,14 @@
1515
#include<unistd.h>
1616

1717
#include"libpq/pqsignal.h"
18+
#include"access/parallel.h"
1819
#include"miscadmin.h"
1920
#include"pgstat.h"
2021
#include"port/atomics.h"
2122
#include"postmaster/bgworker_internals.h"
2223
#include"postmaster/postmaster.h"
2324
#include"replication/logicallauncher.h"
25+
#include"replication/logicalworker.h"
2426
#include"storage/dsm.h"
2527
#include"storage/ipc.h"
2628
#include"storage/latch.h"
@@ -109,14 +111,26 @@ struct BackgroundWorkerHandle
109111
staticBackgroundWorkerArray*BackgroundWorkerData;
110112

111113
/*
112-
* List of workers that are allowed to be started outside of
113-
* shared_preload_libraries.
114+
* List of internal background workers. These are used for mapping the
115+
* function name to actual function when building with EXEC_BACKEND and also
116+
* to allow these to be loaded outside of shared_preload_libraries.
114117
*/
115-
staticconstbgworker_main_typeInternalBGWorkers[]= {
116-
ApplyLauncherMain,
117-
NULL
118+
typedefstructInternalBGWorkerMain
119+
{
120+
char*bgw_function_name;
121+
bgworker_main_typebgw_main;
122+
}InternalBGWorkerMain;
123+
124+
staticconstInternalBGWorkerMainInternalBGWorkers[]= {
125+
{"ParallelWorkerMain",ParallelWorkerMain},
126+
{"ApplyLauncherMain",ApplyLauncherMain},
127+
{"ApplyWorkerMain",ApplyWorkerMain},
128+
/* Dummy entry marking end of the array. */
129+
{NULL,NULL}
118130
};
119131

132+
staticbgworker_main_typeGetInternalBgWorkerMain(BackgroundWorker*worker);
133+
120134
/*
121135
* Calculate shared memory needed.
122136
*/
@@ -341,7 +355,6 @@ BackgroundWorkerStateChange(void)
341355
rw->rw_worker.bgw_flags=slot->worker.bgw_flags;
342356
rw->rw_worker.bgw_start_time=slot->worker.bgw_start_time;
343357
rw->rw_worker.bgw_restart_time=slot->worker.bgw_restart_time;
344-
rw->rw_worker.bgw_main=slot->worker.bgw_main;
345358
rw->rw_worker.bgw_main_arg=slot->worker.bgw_main_arg;
346359
memcpy(rw->rw_worker.bgw_extra,slot->worker.bgw_extra,BGW_EXTRALEN);
347360

@@ -763,17 +776,14 @@ StartBackgroundWorker(void)
763776
}
764777

765778
/*
766-
* If bgw_main is set, we use that value as the initial entrypoint.
767-
* However, if the library containing the entrypoint wasn't loaded at
768-
* postmaster startup time, passing it as a direct function pointer is not
769-
* possible. To work around that, we allow callers for whom a function
770-
* pointer is not available to pass a library name (which will be loaded,
771-
* if necessary) and a function name (which will be looked up in the named
772-
* library).
779+
* For internal workers set the entry point to known function address.
780+
* Otherwise use the entry point specified by library name (which will
781+
* be loaded, if necessary) and a function name (which will be looked up
782+
* in the named library).
773783
*/
774-
if (worker->bgw_main!=NULL)
775-
entrypt=worker->bgw_main;
776-
else
784+
entrypt=GetInternalBgWorkerMain(worker);
785+
786+
if (entrypt==NULL)
777787
entrypt= (bgworker_main_type)
778788
load_external_function(worker->bgw_library_name,
779789
worker->bgw_function_name,
@@ -806,23 +816,13 @@ RegisterBackgroundWorker(BackgroundWorker *worker)
806816
{
807817
RegisteredBgWorker*rw;
808818
staticintnumworkers=0;
809-
boolinternal= false;
810-
inti;
811819

812820
if (!IsUnderPostmaster)
813821
ereport(DEBUG1,
814822
(errmsg("registering background worker \"%s\"",worker->bgw_name)));
815823

816-
for (i=0;InternalBGWorkers[i];i++)
817-
{
818-
if (worker->bgw_main==InternalBGWorkers[i])
819-
{
820-
internal= true;
821-
break;
822-
}
823-
}
824-
825-
if (!process_shared_preload_libraries_in_progress&& !internal)
824+
if (!process_shared_preload_libraries_in_progress&&
825+
GetInternalBgWorkerMain(worker)==NULL)
826826
{
827827
if (!IsUnderPostmaster)
828828
ereport(LOG,
@@ -1152,3 +1152,28 @@ TerminateBackgroundWorker(BackgroundWorkerHandle *handle)
11521152
if (signal_postmaster)
11531153
SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
11541154
}
1155+
1156+
/*
1157+
* Search the known internal worker array and return its main function
1158+
* pointer if found.
1159+
*
1160+
* Returns NULL if not known internal worker.
1161+
*/
1162+
staticbgworker_main_type
1163+
GetInternalBgWorkerMain(BackgroundWorker*worker)
1164+
{
1165+
inti;
1166+
1167+
/* Internal workers always have to use postgres as library name. */
1168+
if (strncmp(worker->bgw_library_name,"postgres",BGW_MAXLEN)!=0)
1169+
returnNULL;
1170+
1171+
for (i=0;InternalBGWorkers[i].bgw_function_name;i++)
1172+
{
1173+
if (strncmp(InternalBGWorkers[i].bgw_function_name,
1174+
worker->bgw_function_name,BGW_MAXLEN)==0)
1175+
returnInternalBGWorkers[i].bgw_main;
1176+
}
1177+
1178+
returnNULL;
1179+
}

‎src/backend/replication/logical/launcher.c

Lines changed: 4 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -295,7 +295,8 @@ logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname, Oid userid,
295295
bgw.bgw_flags=BGWORKER_SHMEM_ACCESS |
296296
BGWORKER_BACKEND_DATABASE_CONNECTION;
297297
bgw.bgw_start_time=BgWorkerStart_RecoveryFinished;
298-
bgw.bgw_main=ApplyWorkerMain;
298+
snprintf(bgw.bgw_library_name,BGW_MAXLEN,"postgres");
299+
snprintf(bgw.bgw_function_name,BGW_MAXLEN,"ApplyWorkerMain");
299300
if (OidIsValid(relid))
300301
snprintf(bgw.bgw_name,BGW_MAXLEN,
301302
"logical replication worker for subscription %u sync %u",subid,relid);
@@ -553,7 +554,8 @@ ApplyLauncherRegister(void)
553554
bgw.bgw_flags=BGWORKER_SHMEM_ACCESS |
554555
BGWORKER_BACKEND_DATABASE_CONNECTION;
555556
bgw.bgw_start_time=BgWorkerStart_RecoveryFinished;
556-
bgw.bgw_main=ApplyLauncherMain;
557+
snprintf(bgw.bgw_library_name,BGW_MAXLEN,"postgres");
558+
snprintf(bgw.bgw_function_name,BGW_MAXLEN,"ApplyLauncherMain");
557559
snprintf(bgw.bgw_name,BGW_MAXLEN,
558560
"logical replication launcher");
559561
bgw.bgw_restart_time=5;

‎src/include/access/parallel.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -67,4 +67,6 @@ extern void AtEOXact_Parallel(bool isCommit);
6767
externvoidAtEOSubXact_Parallel(boolisCommit,SubTransactionIdmySubId);
6868
externvoidParallelWorkerReportLastRecEnd(XLogRecPtrlast_xlog_end);
6969

70+
externvoidParallelWorkerMain(Datummain_arg);
71+
7072
#endif/* PARALLEL_H */

‎src/include/postmaster/bgworker.h

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -91,9 +91,8 @@ typedef struct BackgroundWorker
9191
intbgw_flags;
9292
BgWorkerStartTimebgw_start_time;
9393
intbgw_restart_time;/* in seconds, or BGW_NEVER_RESTART */
94-
bgworker_main_typebgw_main;
95-
charbgw_library_name[BGW_MAXLEN];/* only if bgw_main is NULL */
96-
charbgw_function_name[BGW_MAXLEN];/* only if bgw_main is NULL */
94+
charbgw_library_name[BGW_MAXLEN];
95+
charbgw_function_name[BGW_MAXLEN];
9796
Datumbgw_main_arg;
9897
charbgw_extra[BGW_EXTRALEN];
9998
pid_tbgw_notify_pid;/* SIGUSR1 this backend on start/stop */

‎src/test/modules/test_shm_mq/setup.c

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -216,7 +216,6 @@ setup_background_workers(int nworkers, dsm_segment *seg)
216216
worker.bgw_flags=BGWORKER_SHMEM_ACCESS;
217217
worker.bgw_start_time=BgWorkerStart_ConsistentState;
218218
worker.bgw_restart_time=BGW_NEVER_RESTART;
219-
worker.bgw_main=NULL;/* new worker might not have library loaded */
220219
sprintf(worker.bgw_library_name,"test_shm_mq");
221220
sprintf(worker.bgw_function_name,"test_shm_mq_main");
222221
snprintf(worker.bgw_name,BGW_MAXLEN,"test_shm_mq");

‎src/test/modules/worker_spi/worker_spi.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -347,7 +347,8 @@ _PG_init(void)
347347
BGWORKER_BACKEND_DATABASE_CONNECTION;
348348
worker.bgw_start_time=BgWorkerStart_RecoveryFinished;
349349
worker.bgw_restart_time=BGW_NEVER_RESTART;
350-
worker.bgw_main=worker_spi_main;
350+
sprintf(worker.bgw_library_name,"worker_spi");
351+
sprintf(worker.bgw_function_name,"worker_spi_main");
351352
worker.bgw_notify_pid=0;
352353

353354
/*
@@ -378,7 +379,6 @@ worker_spi_launch(PG_FUNCTION_ARGS)
378379
BGWORKER_BACKEND_DATABASE_CONNECTION;
379380
worker.bgw_start_time=BgWorkerStart_RecoveryFinished;
380381
worker.bgw_restart_time=BGW_NEVER_RESTART;
381-
worker.bgw_main=NULL;/* new worker might not have library loaded */
382382
sprintf(worker.bgw_library_name,"worker_spi");
383383
sprintf(worker.bgw_function_name,"worker_spi_main");
384384
snprintf(worker.bgw_name,BGW_MAXLEN,"worker %d",i);

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