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Centralize decision-making about where to get a backend's PGPROC.

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This code was originally written as part of parallel query effort, but
it seems to have independent value, because if we make one decision
about where to get a PGPROC when we allocate and then put it back on a
different list at backend-exit time, bad things happen.  This isn't
just a theoretical risk; we fixed an actual problem of this type in
commit e280c630a87e1b8325770c6073097d109d79a00f.
This commit is contained in:
Robert Haas 2015-07-28 14:51:57 -04:00
parent 95f4e59c32
commit 6f2871f12e
2 changed files with 27 additions and 29 deletions
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55
src/backend/storage/lmgr/proc.c
View File

@ -242,18 +242,21 @@ InitProcGlobal(void)
/* PGPROC for normal backend, add to freeProcs list */
procs[i].links.next = (SHM_QUEUE *) ProcGlobal->freeProcs;
ProcGlobal->freeProcs = &procs[i];
procs[i].procgloballist = &ProcGlobal->freeProcs;
}
else if (i < MaxConnections + autovacuum_max_workers + 1)
{
/* PGPROC for AV launcher/worker, add to autovacFreeProcs list */
procs[i].links.next = (SHM_QUEUE *) ProcGlobal->autovacFreeProcs;
ProcGlobal->autovacFreeProcs = &procs[i];
procs[i].procgloballist = &ProcGlobal->autovacFreeProcs;
}
else if (i < MaxBackends)
{
/* PGPROC for bgworker, add to bgworkerFreeProcs list */
procs[i].links.next = (SHM_QUEUE *) ProcGlobal->bgworkerFreeProcs;
ProcGlobal->bgworkerFreeProcs = &procs[i];
procs[i].procgloballist = &ProcGlobal->bgworkerFreeProcs;
}
/* Initialize myProcLocks[] shared memory queues. */
@ -281,6 +284,7 @@ InitProcess(void)
{
/* use volatile pointer to prevent code rearrangement */
volatile PROC_HDR *procglobal = ProcGlobal;
PGPROC * volatile * procgloballist;
/*
* ProcGlobal should be set up already (if we are a backend, we inherit
@ -292,9 +296,17 @@ InitProcess(void)
if (MyProc != NULL)
elog(ERROR, "you already exist");
/* Decide which list should supply our PGPROC. */
if (IsAnyAutoVacuumProcess())
procgloballist = &procglobal->autovacFreeProcs;
else if (IsBackgroundWorker)
procgloballist = &procglobal->bgworkerFreeProcs;
else
procgloballist = &procglobal->freeProcs;
/*
* Try to get a proc struct from the free list. If this fails, we must be
* out of PGPROC structures (not to mention semaphores).
* Try to get a proc struct from the appropriate free list. If this
* fails, we must be out of PGPROC structures (not to mention semaphores).
*
* While we are holding the ProcStructLock, also copy the current shared
* estimate of spins_per_delay to local storage.
@ -303,21 +315,11 @@ InitProcess(void)
set_spins_per_delay(procglobal->spins_per_delay);
if (IsAnyAutoVacuumProcess())
MyProc = procglobal->autovacFreeProcs;
else if (IsBackgroundWorker)
MyProc = procglobal->bgworkerFreeProcs;
else
MyProc = procglobal->freeProcs;
MyProc = *procgloballist;
if (MyProc != NULL)
{
if (IsAnyAutoVacuumProcess())
procglobal->autovacFreeProcs = (PGPROC *) MyProc->links.next;
else if (IsBackgroundWorker)
procglobal->bgworkerFreeProcs = (PGPROC *) MyProc->links.next;
else
procglobal->freeProcs = (PGPROC *) MyProc->links.next;
*procgloballist = (PGPROC *) MyProc->links.next;
SpinLockRelease(ProcStructLock);
}
else
@ -335,6 +337,12 @@ InitProcess(void)
}
MyPgXact = &ProcGlobal->allPgXact[MyProc->pgprocno];
/*
* Cross-check that the PGPROC is of the type we expect; if this were
* not the case, it would get returned to the wrong list.
*/
Assert(MyProc->procgloballist == procgloballist);
/*
* Now that we have a PGPROC, mark ourselves as an active postmaster
* child; this is so that the postmaster can detect it if we exit without
@ -761,6 +769,7 @@ ProcKill(int code, Datum arg)
/* use volatile pointer to prevent code rearrangement */
volatile PROC_HDR *procglobal = ProcGlobal;
PGPROC *proc;
PGPROC * volatile * procgloballist;
Assert(MyProc != NULL);
@ -799,24 +808,12 @@ ProcKill(int code, Datum arg)
MyProc = NULL;
DisownLatch(&proc->procLatch);
procgloballist = proc->procgloballist;
SpinLockAcquire(ProcStructLock);
/* Return PGPROC structure (and semaphore) to appropriate freelist */
if (IsAnyAutoVacuumProcess())
{
proc->links.next = (SHM_QUEUE *) procglobal->autovacFreeProcs;
procglobal->autovacFreeProcs = proc;
}
else if (IsBackgroundWorker)
{
proc->links.next = (SHM_QUEUE *) procglobal->bgworkerFreeProcs;
procglobal->bgworkerFreeProcs = proc;
}
else
{
proc->links.next = (SHM_QUEUE *) procglobal->freeProcs;
procglobal->freeProcs = proc;
}
proc->links.next = (SHM_QUEUE *) *procgloballist;
*procgloballist = proc;
/* Update shared estimate of spins_per_delay */
procglobal->spins_per_delay = update_spins_per_delay(procglobal->spins_per_delay);

1
src/include/storage/proc.h
View File

@ -78,6 +78,7 @@ struct PGPROC
{
/* proc->links MUST BE FIRST IN STRUCT (see ProcSleep,ProcWakeup,etc) */
SHM_QUEUE links; /* list link if process is in a list */
PGPROC **procgloballist; /* procglobal list that owns this PGPROC */
PGSemaphoreData sem; /* ONE semaphore to sleep on */
int waitStatus; /* STATUS_WAITING, STATUS_OK or STATUS_ERROR */