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Commit6f2871f

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Centralize decision-making about where to get a backend's PGPROC.
This code was originally written as part of parallel query effort, butit seems to have independent value, because if we make one decisionabout where to get a PGPROC when we allocate and then put it back on adifferent list at backend-exit time, bad things happen. This isn'tjust a theoretical risk; we fixed an actual problem of this type incommite280c63.
1 parent95f4e59 commit6f2871f

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2 files changed

+27
-29
lines changed

2 files changed

+27
-29
lines changed

‎src/backend/storage/lmgr/proc.c

Lines changed: 26 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -242,18 +242,21 @@ InitProcGlobal(void)
242242
/* PGPROC for normal backend, add to freeProcs list */
243243
procs[i].links.next= (SHM_QUEUE*)ProcGlobal->freeProcs;
244244
ProcGlobal->freeProcs=&procs[i];
245+
procs[i].procgloballist=&ProcGlobal->freeProcs;
245246
}
246247
elseif (i<MaxConnections+autovacuum_max_workers+1)
247248
{
248249
/* PGPROC for AV launcher/worker, add to autovacFreeProcs list */
249250
procs[i].links.next= (SHM_QUEUE*)ProcGlobal->autovacFreeProcs;
250251
ProcGlobal->autovacFreeProcs=&procs[i];
252+
procs[i].procgloballist=&ProcGlobal->autovacFreeProcs;
251253
}
252254
elseif (i<MaxBackends)
253255
{
254256
/* PGPROC for bgworker, add to bgworkerFreeProcs list */
255257
procs[i].links.next= (SHM_QUEUE*)ProcGlobal->bgworkerFreeProcs;
256258
ProcGlobal->bgworkerFreeProcs=&procs[i];
259+
procs[i].procgloballist=&ProcGlobal->bgworkerFreeProcs;
257260
}
258261

259262
/* Initialize myProcLocks[] shared memory queues. */
@@ -281,6 +284,7 @@ InitProcess(void)
281284
{
282285
/* use volatile pointer to prevent code rearrangement */
283286
volatilePROC_HDR*procglobal=ProcGlobal;
287+
PGPROC*volatile*procgloballist;
284288

285289
/*
286290
* ProcGlobal should be set up already (if we are a backend, we inherit
@@ -292,9 +296,17 @@ InitProcess(void)
292296
if (MyProc!=NULL)
293297
elog(ERROR,"you already exist");
294298

299+
/* Decide which list should supply our PGPROC. */
300+
if (IsAnyAutoVacuumProcess())
301+
procgloballist=&procglobal->autovacFreeProcs;
302+
elseif (IsBackgroundWorker)
303+
procgloballist=&procglobal->bgworkerFreeProcs;
304+
else
305+
procgloballist=&procglobal->freeProcs;
306+
295307
/*
296-
* Try to get a proc struct from the free list. If this fails, we must be
297-
* out of PGPROC structures (not to mention semaphores).
308+
* Try to get a proc struct from theappropriatefree list. If this
309+
*fails, we must beout of PGPROC structures (not to mention semaphores).
298310
*
299311
* While we are holding the ProcStructLock, also copy the current shared
300312
* estimate of spins_per_delay to local storage.
@@ -303,21 +315,11 @@ InitProcess(void)
303315

304316
set_spins_per_delay(procglobal->spins_per_delay);
305317

306-
if (IsAnyAutoVacuumProcess())
307-
MyProc=procglobal->autovacFreeProcs;
308-
elseif (IsBackgroundWorker)
309-
MyProc=procglobal->bgworkerFreeProcs;
310-
else
311-
MyProc=procglobal->freeProcs;
318+
MyProc=*procgloballist;
312319

313320
if (MyProc!=NULL)
314321
{
315-
if (IsAnyAutoVacuumProcess())
316-
procglobal->autovacFreeProcs= (PGPROC*)MyProc->links.next;
317-
elseif (IsBackgroundWorker)
318-
procglobal->bgworkerFreeProcs= (PGPROC*)MyProc->links.next;
319-
else
320-
procglobal->freeProcs= (PGPROC*)MyProc->links.next;
322+
*procgloballist= (PGPROC*)MyProc->links.next;
321323
SpinLockRelease(ProcStructLock);
322324
}
323325
else
@@ -335,6 +337,12 @@ InitProcess(void)
335337
}
336338
MyPgXact=&ProcGlobal->allPgXact[MyProc->pgprocno];
337339

340+
/*
341+
* Cross-check that the PGPROC is of the type we expect; if this were
342+
* not the case, it would get returned to the wrong list.
343+
*/
344+
Assert(MyProc->procgloballist==procgloballist);
345+
338346
/*
339347
* Now that we have a PGPROC, mark ourselves as an active postmaster
340348
* child; this is so that the postmaster can detect it if we exit without
@@ -761,6 +769,7 @@ ProcKill(int code, Datum arg)
761769
/* use volatile pointer to prevent code rearrangement */
762770
volatilePROC_HDR*procglobal=ProcGlobal;
763771
PGPROC*proc;
772+
PGPROC*volatile*procgloballist;
764773

765774
Assert(MyProc!=NULL);
766775

@@ -799,24 +808,12 @@ ProcKill(int code, Datum arg)
799808
MyProc=NULL;
800809
DisownLatch(&proc->procLatch);
801810

811+
procgloballist=proc->procgloballist;
802812
SpinLockAcquire(ProcStructLock);
803813

804814
/* Return PGPROC structure (and semaphore) to appropriate freelist */
805-
if (IsAnyAutoVacuumProcess())
806-
{
807-
proc->links.next= (SHM_QUEUE*)procglobal->autovacFreeProcs;
808-
procglobal->autovacFreeProcs=proc;
809-
}
810-
elseif (IsBackgroundWorker)
811-
{
812-
proc->links.next= (SHM_QUEUE*)procglobal->bgworkerFreeProcs;
813-
procglobal->bgworkerFreeProcs=proc;
814-
}
815-
else
816-
{
817-
proc->links.next= (SHM_QUEUE*)procglobal->freeProcs;
818-
procglobal->freeProcs=proc;
819-
}
815+
proc->links.next= (SHM_QUEUE*)*procgloballist;
816+
*procgloballist=proc;
820817

821818
/* Update shared estimate of spins_per_delay */
822819
procglobal->spins_per_delay=update_spins_per_delay(procglobal->spins_per_delay);

‎src/include/storage/proc.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -78,6 +78,7 @@ struct PGPROC
7878
{
7979
/* proc->links MUST BE FIRST IN STRUCT (see ProcSleep,ProcWakeup,etc) */
8080
SHM_QUEUElinks;/* list link if process is in a list */
81+
PGPROC**procgloballist;/* procglobal list that owns this PGPROC */
8182

8283
PGSemaphoreDatasem;/* ONE semaphore to sleep on */
8384
intwaitStatus;/* STATUS_WAITING, STATUS_OK or STATUS_ERROR */

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