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Commit869f693

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On Windows, ensure shared memory handle gets closed if not being used.
Postmaster child processes that aren't supposed to be attached to sharedmemory were not bothering to close the shared memory mapping handle theyinherit from the postmaster process. That's mostly harmless, since thehandle vanishes anyway when the child process exits -- but the sysloggerprocess, if used, doesn't get killed and restarted during recovery from abackend crash. That meant that Windows doesn't see the shared memorymapping as becoming free, so it doesn't delete it and the postmaster isunable to create a new one, resulting in failure to recover from crasheswhenever logging_collector is turned on.Per report from Dmitry Vasilyev. It's a bit astonishing that we'd notfigured this out long ago, since it's been broken from the very beginningsof out native Windows support; probably some previously-unexplained troublereports trace to this.A secondary problem is that on Cygwin (perhaps only in older versions?),exec() may not detach from the shared memory segment after all, in whichcase these child processes did remain attached to shared memory, posingthe risk of an unexpected shared memory clobber if they went off the railssomehow. That may be a long-gone bug, but we can deal with it now if it'sstill live, by detaching within the infrastructure introduced here to dealwith closing the handle.Back-patch to all supported branches.Tom Lane and Amit Kapila
1 parent6bcce25 commit869f693

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4 files changed

+116
-25
lines changed

4 files changed

+116
-25
lines changed

‎src/backend/port/sysv_shmem.c

Lines changed: 45 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -195,7 +195,7 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
195195

196196
/****************************************************************************/
197197
/*IpcMemoryDetach(status, shmaddr)removes a shared memory segment*/
198-
/*from process' addressspaceq*/
198+
/*from process' addressspace*/
199199
/*(called as an on_shmem_exit callback, hence funny argument list)*/
200200
/****************************************************************************/
201201
staticvoid
@@ -583,9 +583,10 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port,
583583
/*
584584
* PGSharedMemoryReAttach
585585
*
586-
* Re-attach to an already existing shared memory segment. In the non
587-
* EXEC_BACKEND case this is not used, because postmaster children inherit
588-
* the shared memory segment attachment via fork().
586+
* This is called during startup of a postmaster child process to re-attach to
587+
* an already existing shared memory segment. This is needed only in the
588+
* EXEC_BACKEND case; otherwise postmaster children inherit the shared memory
589+
* segment attachment via fork().
589590
*
590591
* UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
591592
* routine. The caller must have already restored them to the postmaster's
@@ -619,16 +620,52 @@ PGSharedMemoryReAttach(void)
619620

620621
UsedShmemSegAddr=hdr;/* probably redundant */
621622
}
623+
624+
/*
625+
* PGSharedMemoryNoReAttach
626+
*
627+
* This is called during startup of a postmaster child process when we choose
628+
* *not* to re-attach to the existing shared memory segment. We must clean up
629+
* to leave things in the appropriate state. This is not used in the non
630+
* EXEC_BACKEND case, either.
631+
*
632+
* The child process startup logic might or might not call PGSharedMemoryDetach
633+
* after this; make sure that it will be a no-op if called.
634+
*
635+
* UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
636+
* routine. The caller must have already restored them to the postmaster's
637+
* values.
638+
*/
639+
void
640+
PGSharedMemoryNoReAttach(void)
641+
{
642+
Assert(UsedShmemSegAddr!=NULL);
643+
Assert(IsUnderPostmaster);
644+
645+
#ifdef__CYGWIN__
646+
/* cygipc (currently) appears to not detach on exec. */
647+
PGSharedMemoryDetach();
648+
#endif
649+
650+
/* For cleanliness, reset UsedShmemSegAddr to show we're not attached. */
651+
UsedShmemSegAddr=NULL;
652+
/* And the same for UsedShmemSegID. */
653+
UsedShmemSegID=0;
654+
}
655+
622656
#endif/* EXEC_BACKEND */
623657

624658
/*
625659
* PGSharedMemoryDetach
626660
*
627661
* Detach from the shared memory segment, if still attached. This is not
628-
* intended for use by the process that originally created the segment
629-
* (it will have an on_shmem_exit callback registered to do that). Rather,
630-
* this is for subprocesses that have inherited an attachment and want to
631-
* get rid of it.
662+
* intended to be called explicitly by the process that originally created the
663+
* segment (it will have an on_shmem_exit callback registered to do that).
664+
* Rather, this is for subprocesses that have inherited an attachment and want
665+
* to get rid of it.
666+
*
667+
* UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
668+
* routine.
632669
*/
633670
void
634671
PGSharedMemoryDetach(void)

‎src/backend/port/win32_shmem.c

Lines changed: 66 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -17,7 +17,7 @@
1717
#include"storage/ipc.h"
1818
#include"storage/pg_shmem.h"
1919

20-
HANDLEUsedShmemSegID=0;
20+
HANDLEUsedShmemSegID=INVALID_HANDLE_VALUE;
2121
void*UsedShmemSegAddr=NULL;
2222
staticSizeUsedShmemSegSize=0;
2323

@@ -83,7 +83,6 @@ GetSharedMemName(void)
8383
* we only care about shmem segments that are associated with the intended
8484
* DataDir. This is an important consideration since accidental matches of
8585
* shmem segment IDs are reasonably common.
86-
*
8786
*/
8887
bool
8988
PGSharedMemoryIsInUse(unsigned longid1,unsigned longid2)
@@ -115,7 +114,6 @@ PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
115114
* or recycle any existing segment. On win32, we always create a new segment,
116115
* since there is no need for recycling (segments go away automatically
117116
* when the last backend exits)
118-
*
119117
*/
120118
PGShmemHeader*
121119
PGSharedMemoryCreate(Sizesize,boolmakePrivate,intport,
@@ -218,9 +216,6 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port,
218216
elog(LOG,"could not close handle to shared memory: error code %lu",GetLastError());
219217

220218

221-
/* Register on-exit routine to delete the new segment */
222-
on_shmem_exit(pgwin32_SharedMemoryDelete,PointerGetDatum(hmap2));
223-
224219
/*
225220
* Get a pointer to the new shared memory segment. Map the whole segment
226221
* at once, and let the system decide on the initial address.
@@ -254,15 +249,19 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port,
254249
UsedShmemSegSize=size;
255250
UsedShmemSegID=hmap2;
256251

252+
/* Register on-exit routine to delete the new segment */
253+
on_shmem_exit(pgwin32_SharedMemoryDelete,PointerGetDatum(hmap2));
254+
257255
*shim=hdr;
258256
returnhdr;
259257
}
260258

261259
/*
262260
* PGSharedMemoryReAttach
263261
*
264-
* Re-attach to an already existing shared memory segment. Use the
265-
* handle inherited from the postmaster.
262+
* This is called during startup of a postmaster child process to re-attach to
263+
* an already existing shared memory segment, using the handle inherited from
264+
* the postmaster.
266265
*
267266
* UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
268267
* routine. The caller must have already restored them to the postmaster's
@@ -298,37 +297,88 @@ PGSharedMemoryReAttach(void)
298297
UsedShmemSegAddr=hdr;/* probably redundant */
299298
}
300299

300+
/*
301+
* PGSharedMemoryNoReAttach
302+
*
303+
* This is called during startup of a postmaster child process when we choose
304+
* *not* to re-attach to the existing shared memory segment. We must clean up
305+
* to leave things in the appropriate state.
306+
*
307+
* The child process startup logic might or might not call PGSharedMemoryDetach
308+
* after this; make sure that it will be a no-op if called.
309+
*
310+
* UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
311+
* routine. The caller must have already restored them to the postmaster's
312+
* values.
313+
*/
314+
void
315+
PGSharedMemoryNoReAttach(void)
316+
{
317+
Assert(UsedShmemSegAddr!=NULL);
318+
Assert(IsUnderPostmaster);
319+
320+
/*
321+
* Under Windows we will not have mapped the segment, so we don't need to
322+
* un-map it. Just reset UsedShmemSegAddr to show we're not attached.
323+
*/
324+
UsedShmemSegAddr=NULL;
325+
326+
/*
327+
* We *must* close the inherited shmem segment handle, else Windows will
328+
* consider the existence of this process to mean it can't release the
329+
* shmem segment yet. We can now use PGSharedMemoryDetach to do that.
330+
*/
331+
PGSharedMemoryDetach();
332+
}
333+
301334
/*
302335
* PGSharedMemoryDetach
303336
*
304337
* Detach from the shared memory segment, if still attached. This is not
305-
* intended for use by the process that originally created the segment. Rather,
306-
* this is for subprocesses that have inherited an attachment and want to
307-
* get rid of it.
338+
* intended to be called explicitly by the process that originally created the
339+
* segment (it will have an on_shmem_exit callback registered to do that).
340+
* Rather, this is for subprocesses that have inherited an attachment and want
341+
* to get rid of it.
342+
*
343+
* UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
344+
* routine.
308345
*/
309346
void
310347
PGSharedMemoryDetach(void)
311348
{
349+
/* Unmap the view, if it's mapped */
312350
if (UsedShmemSegAddr!=NULL)
313351
{
314352
if (!UnmapViewOfFile(UsedShmemSegAddr))
315-
elog(LOG,"could not unmap view of shared memory: error code %lu",GetLastError());
353+
elog(LOG,"could not unmap view of shared memory: error code %lu",
354+
GetLastError());
316355

317356
UsedShmemSegAddr=NULL;
318357
}
358+
359+
/* And close the shmem handle, if we have one */
360+
if (UsedShmemSegID!=INVALID_HANDLE_VALUE)
361+
{
362+
if (!CloseHandle(UsedShmemSegID))
363+
elog(LOG,"could not close handle to shared memory: error code %lu",
364+
GetLastError());
365+
366+
UsedShmemSegID=INVALID_HANDLE_VALUE;
367+
}
319368
}
320369

321370

322371
/*
323-
*pgwin32_SharedMemoryDelete(status, shmId)deletes a shared memory segment
324-
*(called as an on_shmem_exit callback, hence funny argument list)
372+
* pgwin32_SharedMemoryDelete
373+
*
374+
* Detach from and delete the shared memory segment
375+
* (called as an on_shmem_exit callback, hence funny argument list)
325376
*/
326377
staticvoid
327378
pgwin32_SharedMemoryDelete(intstatus,DatumshmId)
328379
{
380+
Assert(DatumGetPointer(shmId)==UsedShmemSegID);
329381
PGSharedMemoryDetach();
330-
if (!CloseHandle(DatumGetPointer(shmId)))
331-
elog(LOG,"could not close handle to shared memory: error code %lu",GetLastError());
332382
}
333383

334384
/*

‎src/backend/postmaster/postmaster.c

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4628,14 +4628,17 @@ SubPostmasterMain(int argc, char *argv[])
46284628
/*
46294629
* If appropriate, physically re-attach to shared memory segment. We want
46304630
* to do this before going any further to ensure that we can attach at the
4631-
* same address the postmaster used.
4631+
* same address the postmaster used. On the other hand, if we choose not
4632+
* to re-attach, we may have other cleanup to do.
46324633
*/
46334634
if (strcmp(argv[1],"--forkbackend")==0||
46344635
strcmp(argv[1],"--forkavlauncher")==0||
46354636
strcmp(argv[1],"--forkavworker")==0||
46364637
strcmp(argv[1],"--forkboot")==0||
46374638
strncmp(argv[1],"--forkbgworker=",15)==0)
46384639
PGSharedMemoryReAttach();
4640+
else
4641+
PGSharedMemoryNoReAttach();
46394642

46404643
/* autovacuum needs this set before calling InitProcess */
46414644
if (strcmp(argv[1],"--forkavlauncher")==0)

‎src/include/storage/pg_shmem.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -61,6 +61,7 @@ extern void *UsedShmemSegAddr;
6161

6262
#ifdefEXEC_BACKEND
6363
externvoidPGSharedMemoryReAttach(void);
64+
externvoidPGSharedMemoryNoReAttach(void);
6465
#endif
6566

6667
externPGShmemHeader*PGSharedMemoryCreate(Sizesize,boolmakePrivate,

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