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Commit7de19fb

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Use data directory inode number, not port, to select SysV resource keys.
This approach provides a much tighter binding between a data directoryand the associated SysV shared memory block (and SysV or named-POSIXsemaphores, if we're using those). Key collisions are still possible,but only between data directories stored on different filesystems,so the situation should be negligible in practice. More importantly,restarting the postmaster with a different port number no longerrisks failing to identify a relevant shared memory block, even whenpostmaster.pid has been removed. A standalone backend is likewisemuch more certain to detect conflicting leftover backends.(In the longer term, we might now think about deprecating the port asa cluster-wide value, so that one postmaster could support socketswith varying port numbers. But that's for another day.)The hazards fixed here apply only on Unix systems; our Windows codepaths already use identifiers derived from the data directory pathname rather than the port.src/test/recovery/t/017_shm.pl, which intends to test key-collisioncases, has been substantially rewritten since it can no longer usetwo postmasters with identical port numbers to trigger the case.Instead, use Perl's IPC::SharedMem module to create a conflictingshmem segment directly. The test script will be skipped if thatmodule is not available. (This means that some older buildfarmmembers won't run it, but I don't think that that results in anymeaningful coverage loss.)Patch by me; thanks to Noah Misch and Peter Eisentraut for discussionand review.Discussion:https://postgr.es/m/16908.1557521200@sss.pgh.pa.us
1 parent8b94dab commit7de19fb

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12 files changed

+159
-124
lines changed

12 files changed

+159
-124
lines changed

‎src/backend/port/posix_sema.c

Lines changed: 17 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -29,6 +29,7 @@
2929
#include<semaphore.h>
3030
#include<signal.h>
3131
#include<unistd.h>
32+
#include<sys/stat.h>
3233

3334
#include"miscadmin.h"
3435
#include"storage/ipc.h"
@@ -181,10 +182,6 @@ PGSemaphoreShmemSize(int maxSemas)
181182
* are acquired here or in PGSemaphoreCreate, register an on_shmem_exit
182183
* callback to release them.
183184
*
184-
* The port number is passed for possible use as a key (for Posix, we use
185-
* it to generate the starting semaphore name). In a standalone backend,
186-
* zero will be passed.
187-
*
188185
* In the Posix implementation, we acquire semaphores on-demand; the
189186
* maxSemas parameter is just used to size the arrays. For unnamed
190187
* semaphores, there is an array of PGSemaphoreData structs in shared memory.
@@ -196,8 +193,22 @@ PGSemaphoreShmemSize(int maxSemas)
196193
* we don't have to expose the counters to other processes.)
197194
*/
198195
void
199-
PGReserveSemaphores(intmaxSemas,intport)
196+
PGReserveSemaphores(intmaxSemas)
200197
{
198+
structstatstatbuf;
199+
200+
/*
201+
* We use the data directory's inode number to seed the search for free
202+
* semaphore keys. This minimizes the odds of collision with other
203+
* postmasters, while maximizing the odds that we will detect and clean up
204+
* semaphores left over from a crashed postmaster in our own directory.
205+
*/
206+
if (stat(DataDir,&statbuf)<0)
207+
ereport(FATAL,
208+
(errcode_for_file_access(),
209+
errmsg("could not stat data directory \"%s\": %m",
210+
DataDir)));
211+
201212
#ifdefUSE_NAMED_POSIX_SEMAPHORES
202213
mySemPointers= (sem_t**)malloc(maxSemas*sizeof(sem_t*));
203214
if (mySemPointers==NULL)
@@ -215,7 +226,7 @@ PGReserveSemaphores(int maxSemas, int port)
215226

216227
numSems=0;
217228
maxSems=maxSemas;
218-
nextSemKey=port*1000;
229+
nextSemKey=statbuf.st_ino;
219230

220231
on_shmem_exit(ReleaseSemaphores,0);
221232
}

‎src/backend/port/sysv_sema.c

Lines changed: 17 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -17,6 +17,7 @@
1717
#include<signal.h>
1818
#include<unistd.h>
1919
#include<sys/file.h>
20+
#include<sys/stat.h>
2021
#ifdefHAVE_SYS_IPC_H
2122
#include<sys/ipc.h>
2223
#endif
@@ -301,10 +302,6 @@ PGSemaphoreShmemSize(int maxSemas)
301302
* are acquired here or in PGSemaphoreCreate, register an on_shmem_exit
302303
* callback to release them.
303304
*
304-
* The port number is passed for possible use as a key (for SysV, we use
305-
* it to generate the starting semaphore key). In a standalone backend,
306-
* zero will be passed.
307-
*
308305
* In the SysV implementation, we acquire semaphore sets on-demand; the
309306
* maxSemas parameter is just used to size the arrays. There is an array
310307
* of PGSemaphoreData structs in shared memory, and a postmaster-local array
@@ -314,8 +311,22 @@ PGSemaphoreShmemSize(int maxSemas)
314311
* have clobbered.)
315312
*/
316313
void
317-
PGReserveSemaphores(intmaxSemas,intport)
314+
PGReserveSemaphores(intmaxSemas)
318315
{
316+
structstatstatbuf;
317+
318+
/*
319+
* We use the data directory's inode number to seed the search for free
320+
* semaphore keys. This minimizes the odds of collision with other
321+
* postmasters, while maximizing the odds that we will detect and clean up
322+
* semaphores left over from a crashed postmaster in our own directory.
323+
*/
324+
if (stat(DataDir,&statbuf)<0)
325+
ereport(FATAL,
326+
(errcode_for_file_access(),
327+
errmsg("could not stat data directory \"%s\": %m",
328+
DataDir)));
329+
319330
/*
320331
* We must use ShmemAllocUnlocked(), since the spinlock protecting
321332
* ShmemAlloc() won't be ready yet. (This ordering is necessary when we
@@ -332,7 +343,7 @@ PGReserveSemaphores(int maxSemas, int port)
332343
if (mySemaSets==NULL)
333344
elog(PANIC,"out of memory");
334345
numSemaSets=0;
335-
nextSemaKey=port*1000;
346+
nextSemaKey=statbuf.st_ino;
336347
nextSemaNumber=SEMAS_PER_SET;/* force sema set alloc on 1st call */
337348

338349
on_shmem_exit(ReleaseSemaphores,0);

‎src/backend/port/sysv_shmem.c

Lines changed: 21 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -390,11 +390,12 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
390390

391391
/*
392392
* Try to attach to the segment and see if it matches our data directory.
393-
* This avoids key-conflict problems on machines that are running several
394-
* postmasters under the same userid and port number. (That would not
395-
* ordinarily happen in production, but it can happen during parallel
396-
* testing. Since our test setups don't open any TCP ports on Unix, such
397-
* cases don't conflict otherwise.)
393+
* This avoids any risk of duplicate-shmem-key conflicts on machines that
394+
* are running several postmasters under the same userid.
395+
*
396+
* (When we're called from PGSharedMemoryCreate, this stat call is
397+
* duplicative; but since this isn't a high-traffic case it's not worth
398+
* trying to optimize.)
398399
*/
399400
if (stat(DataDir,&statbuf)<0)
400401
returnSHMSTATE_ANALYSIS_FAILURE;/* can't stat; be conservative */
@@ -617,12 +618,9 @@ AnonymousShmemDetach(int status, Datum arg)
617618
* we do not fail upon collision with foreign shmem segments. The idea here
618619
* is to detect and re-use keys that may have been assigned by a crashed
619620
* postmaster or backend.
620-
*
621-
* The port number is passed for possible use as a key (for SysV, we use
622-
* it to generate the starting shmem key).
623621
*/
624622
PGShmemHeader*
625-
PGSharedMemoryCreate(Sizesize,intport,
623+
PGSharedMemoryCreate(Sizesize,
626624
PGShmemHeader**shim)
627625
{
628626
IpcMemoryKeyNextShmemSegID;
@@ -631,6 +629,17 @@ PGSharedMemoryCreate(Size size, int port,
631629
structstatstatbuf;
632630
Sizesysvsize;
633631

632+
/*
633+
* We use the data directory's ID info (inode and device numbers) to
634+
* positively identify shmem segments associated with this data dir, and
635+
* also as seeds for searching for a free shmem key.
636+
*/
637+
if (stat(DataDir,&statbuf)<0)
638+
ereport(FATAL,
639+
(errcode_for_file_access(),
640+
errmsg("could not stat data directory \"%s\": %m",
641+
DataDir)));
642+
634643
/* Complain if hugepages demanded but we can't possibly support them */
635644
#if !defined(MAP_HUGETLB)
636645
if (huge_pages==HUGE_PAGES_ON)
@@ -659,10 +668,10 @@ PGSharedMemoryCreate(Size size, int port,
659668
/*
660669
* Loop till we find a free IPC key. Trust CreateDataDirLockFile() to
661670
* ensure no more than one postmaster per data directory can enter this
662-
* loop simultaneously. (CreateDataDirLockFile() does notensure that,
663-
* but prefer fixing it over coping here.)
671+
* loop simultaneously. (CreateDataDirLockFile() does notentirely ensure
672+
*that,but prefer fixing it over coping here.)
664673
*/
665-
NextShmemSegID=1+port*1000;
674+
NextShmemSegID=statbuf.st_ino;
666675

667676
for (;;)
668677
{
@@ -748,11 +757,6 @@ PGSharedMemoryCreate(Size size, int port,
748757
hdr->dsm_control=0;
749758

750759
/* Fill in the data directory ID info, too */
751-
if (stat(DataDir,&statbuf)<0)
752-
ereport(FATAL,
753-
(errcode_for_file_access(),
754-
errmsg("could not stat data directory \"%s\": %m",
755-
DataDir)));
756760
hdr->device=statbuf.st_dev;
757761
hdr->inode=statbuf.st_ino;
758762

‎src/backend/port/win32_sema.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -44,7 +44,7 @@ PGSemaphoreShmemSize(int maxSemas)
4444
* process exits.
4545
*/
4646
void
47-
PGReserveSemaphores(intmaxSemas,intport)
47+
PGReserveSemaphores(intmaxSemas)
4848
{
4949
mySemSet= (HANDLE*)malloc(maxSemas*sizeof(HANDLE));
5050
if (mySemSet==NULL)

‎src/backend/port/win32_shmem.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -194,7 +194,7 @@ EnableLockPagesPrivilege(int elevel)
194194
* standard header.
195195
*/
196196
PGShmemHeader*
197-
PGSharedMemoryCreate(Sizesize,intport,
197+
PGSharedMemoryCreate(Sizesize,
198198
PGShmemHeader**shim)
199199
{
200200
void*memAddress;

‎src/backend/postmaster/postmaster.c

Lines changed: 12 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -385,7 +385,7 @@ static void getInstallationPaths(const char *argv0);
385385
staticvoidcheckControlFile(void);
386386
staticPort*ConnCreate(intserverFd);
387387
staticvoidConnFree(Port*port);
388-
staticvoidreset_shared(intport);
388+
staticvoidreset_shared(void);
389389
staticvoidSIGHUP_handler(SIGNAL_ARGS);
390390
staticvoidpmdie(SIGNAL_ARGS);
391391
staticvoidreaper(SIGNAL_ARGS);
@@ -1175,7 +1175,7 @@ PostmasterMain(int argc, char *argv[])
11751175
/*
11761176
* Set up shared memory and semaphores.
11771177
*/
1178-
reset_shared(PostPortNumber);
1178+
reset_shared();
11791179

11801180
/*
11811181
* Estimate number of openable files. This must happen after setting up
@@ -2599,17 +2599,16 @@ InitProcessGlobals(void)
25992599
* reset_shared -- reset shared memory and semaphores
26002600
*/
26012601
staticvoid
2602-
reset_shared(intport)
2602+
reset_shared(void)
26032603
{
26042604
/*
26052605
* Create or re-create shared memory and semaphores.
26062606
*
26072607
* Note: in each "cycle of life" we will normally assign the same IPC keys
2608-
* (if using SysV shmem and/or semas), since the port number is used to
2609-
* determine IPC keys. This helps ensure that we will clean up dead IPC
2610-
* objects if the postmaster crashes and is restarted.
2608+
* (if using SysV shmem and/or semas). This helps ensure that we will
2609+
* clean up dead IPC objects if the postmaster crashes and is restarted.
26112610
*/
2612-
CreateSharedMemoryAndSemaphores(port);
2611+
CreateSharedMemoryAndSemaphores();
26132612
}
26142613

26152614

@@ -3934,7 +3933,7 @@ PostmasterStateMachine(void)
39343933
/* re-read control file into local memory */
39353934
LocalProcessControlFile(true);
39363935

3937-
reset_shared(PostPortNumber);
3936+
reset_shared();
39383937

39393938
StartupPID=StartupDataBase();
39403939
Assert(StartupPID!=0);
@@ -4962,7 +4961,7 @@ SubPostmasterMain(int argc, char *argv[])
49624961
InitProcess();
49634962

49644963
/* Attach process to shared data structures */
4965-
CreateSharedMemoryAndSemaphores(0);
4964+
CreateSharedMemoryAndSemaphores();
49664965

49674966
/* And run the backend */
49684967
BackendRun(&port);/* does not return */
@@ -4976,7 +4975,7 @@ SubPostmasterMain(int argc, char *argv[])
49764975
InitAuxiliaryProcess();
49774976

49784977
/* Attach process to shared data structures */
4979-
CreateSharedMemoryAndSemaphores(0);
4978+
CreateSharedMemoryAndSemaphores();
49804979

49814980
AuxiliaryProcessMain(argc-2,argv+2);/* does not return */
49824981
}
@@ -4989,7 +4988,7 @@ SubPostmasterMain(int argc, char *argv[])
49894988
InitProcess();
49904989

49914990
/* Attach process to shared data structures */
4992-
CreateSharedMemoryAndSemaphores(0);
4991+
CreateSharedMemoryAndSemaphores();
49934992

49944993
AutoVacLauncherMain(argc-2,argv+2);/* does not return */
49954994
}
@@ -5002,7 +5001,7 @@ SubPostmasterMain(int argc, char *argv[])
50025001
InitProcess();
50035002

50045003
/* Attach process to shared data structures */
5005-
CreateSharedMemoryAndSemaphores(0);
5004+
CreateSharedMemoryAndSemaphores();
50065005

50075006
AutoVacWorkerMain(argc-2,argv+2);/* does not return */
50085007
}
@@ -5020,7 +5019,7 @@ SubPostmasterMain(int argc, char *argv[])
50205019
InitProcess();
50215020

50225021
/* Attach process to shared data structures */
5023-
CreateSharedMemoryAndSemaphores(0);
5022+
CreateSharedMemoryAndSemaphores();
50245023

50255024
/* Fetch MyBgworkerEntry from shared memory */
50265025
shmem_slot=atoi(argv[1]+15);

‎src/backend/storage/ipc/ipci.c

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -91,7 +91,7 @@ RequestAddinShmemSpace(Size size)
9191
* This is a bit code-wasteful and could be cleaned up.)
9292
*/
9393
void
94-
CreateSharedMemoryAndSemaphores(intport)
94+
CreateSharedMemoryAndSemaphores(void)
9595
{
9696
PGShmemHeader*shim=NULL;
9797

@@ -163,14 +163,14 @@ CreateSharedMemoryAndSemaphores(int port)
163163
/*
164164
* Create the shmem segment
165165
*/
166-
seghdr=PGSharedMemoryCreate(size,port,&shim);
166+
seghdr=PGSharedMemoryCreate(size,&shim);
167167

168168
InitShmemAccess(seghdr);
169169

170170
/*
171171
* Create semaphores
172172
*/
173-
PGReserveSemaphores(numSemas,port);
173+
PGReserveSemaphores(numSemas);
174174

175175
/*
176176
* If spinlocks are disabled, initialize emulation layer (which

‎src/backend/utils/init/postinit.c

Lines changed: 3 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -445,12 +445,10 @@ InitCommunication(void)
445445
if (!IsUnderPostmaster)/* postmaster already did this */
446446
{
447447
/*
448-
* We're running a postgres bootstrap process or a standalone backend.
449-
* Though we won't listen on PostPortNumber, use it to select a shmem
450-
* key. This increases the chance of detecting a leftover live
451-
* backend of this DataDir.
448+
* We're running a postgres bootstrap process or a standalone backend,
449+
* so we need to set up shmem.
452450
*/
453-
CreateSharedMemoryAndSemaphores(PostPortNumber);
451+
CreateSharedMemoryAndSemaphores();
454452
}
455453
}
456454

‎src/include/storage/ipc.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -76,6 +76,6 @@ extern void on_exit_reset(void);
7676
/* ipci.c */
7777
externPGDLLIMPORTshmem_startup_hook_typeshmem_startup_hook;
7878

79-
externvoidCreateSharedMemoryAndSemaphores(intport);
79+
externvoidCreateSharedMemoryAndSemaphores(void);
8080

8181
#endif/* IPC_H */

‎src/include/storage/pg_sema.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -41,7 +41,7 @@ typedef HANDLE PGSemaphore;
4141
externSizePGSemaphoreShmemSize(intmaxSemas);
4242

4343
/* Module initialization (called during postmaster start or shmem reinit) */
44-
externvoidPGReserveSemaphores(intmaxSemas,intport);
44+
externvoidPGReserveSemaphores(intmaxSemas);
4545

4646
/* Allocate a PGSemaphore structure with initial count 1 */
4747
externPGSemaphorePGSemaphoreCreate(void);

‎src/include/storage/pg_shmem.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -82,7 +82,7 @@ extern void PGSharedMemoryReAttach(void);
8282
externvoidPGSharedMemoryNoReAttach(void);
8383
#endif
8484

85-
externPGShmemHeader*PGSharedMemoryCreate(Sizesize,intport,
85+
externPGShmemHeader*PGSharedMemoryCreate(Sizesize,
8686
PGShmemHeader**shim);
8787
externboolPGSharedMemoryIsInUse(unsigned longid1,unsigned longid2);
8888
externvoidPGSharedMemoryDetach(void);

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