src/backend/access/transam/twophase.c

@@ -485,7 +485,7 @@ MarkAsPreparingGuts(GlobalTransaction gxact, TransactionId xid, const char *gid,
 	proc->roleId = owner;
 	proc->tempNamespaceId = InvalidOid;
 	proc->isBackgroundWorker = false;
-	proc->lwWaiting = LW_WS_NOT_WAITING;
+	proc->lwWaiting = false;
 	proc->lwWaitMode = 0;
 	proc->waitLock = NULL;
 	proc->waitProcLock = NULL;

src/backend/port/win32/socket.c

@@ -290,7 +290,6 @@ pgwin32_socket(int af, int type, int protocol)
 	if (ioctlsocket(s, FIONBIO, &on))
 	{
 		TranslateSocketError();
-		closesocket(s);
 		return INVALID_SOCKET;
 	}
 	errno = 0;

src/backend/storage/lmgr/lwlock.c

@@ -913,15 +913,6 @@ LWLockWakeup(LWLock *lock)
 			wokeup_somebody = true;
 		}
 
-		/*
-		 * Signal that the process isn't on the wait list anymore. This allows
-		 * LWLockDequeueSelf() to remove itself of the waitlist with a
-		 * proclist_delete(), rather than having to check if it has been
-		 * removed from the list.
-		 */
-		Assert(waiter->lwWaiting == LW_WS_WAITING);
-		waiter->lwWaiting = LW_WS_PENDING_WAKEUP;
-
 		/*
 		 * Once we've woken up an exclusive lock, there's no point in waking
 		 * up anybody else.
@@ -979,7 +970,7 @@ LWLockWakeup(LWLock *lock)
 		 * another lock.
 		 */
 		pg_write_barrier();
-		waiter->lwWaiting = LW_WS_NOT_WAITING;
+		waiter->lwWaiting = false;
 		PGSemaphoreUnlock(waiter->sem);
 	}
 }
@@ -1000,7 +991,7 @@ LWLockQueueSelf(LWLock *lock, LWLockMode mode)
 	if (MyProc == NULL)
 		elog(PANIC, "cannot wait without a PGPROC structure");
 
-	if (MyProc->lwWaiting != LW_WS_NOT_WAITING)
+	if (MyProc->lwWaiting)
 		elog(PANIC, "queueing for lock while waiting on another one");
 
 	LWLockWaitListLock(lock);
@@ -1008,7 +999,7 @@ LWLockQueueSelf(LWLock *lock, LWLockMode mode)
 	/* setting the flag is protected by the spinlock */
 	pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_HAS_WAITERS);
 
-	MyProc->lwWaiting = LW_WS_WAITING;
+	MyProc->lwWaiting = true;
 	MyProc->lwWaitMode = mode;
 
 	/* LW_WAIT_UNTIL_FREE waiters are always at the front of the queue */
@@ -1036,7 +1027,8 @@ LWLockQueueSelf(LWLock *lock, LWLockMode mode)
 static void
 LWLockDequeueSelf(LWLock *lock)
 {
-	bool		on_waitlist;
+	bool		found = false;
+	proclist_mutable_iter iter;
 
 #ifdef LWLOCK_STATS
 	lwlock_stats *lwstats;
@@ -1049,13 +1041,18 @@ LWLockDequeueSelf(LWLock *lock)
 	LWLockWaitListLock(lock);
 
 	/*
-	 * Remove ourselves from the waitlist, unless we've already been
-	 * removed. The removal happens with the wait list lock held, so there's
-	 * no race in this check.
+	 * Can't just remove ourselves from the list, but we need to iterate over
+	 * all entries as somebody else could have dequeued us.
 	 */
-	on_waitlist = MyProc->lwWaiting == LW_WS_WAITING;
-	if (on_waitlist)
-		proclist_delete(&lock->waiters, MyProc->pgprocno, lwWaitLink);
+	proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
+	{
+		if (iter.cur == MyProc->pgprocno)
+		{
+			found = true;
+			proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
+			break;
+		}
+	}
 
 	if (proclist_is_empty(&lock->waiters) &&
 		(pg_atomic_read_u32(&lock->state) & LW_FLAG_HAS_WAITERS) != 0)
@@ -1067,8 +1064,8 @@ LWLockDequeueSelf(LWLock *lock)
 	LWLockWaitListUnlock(lock);
 
 	/* clear waiting state again, nice for debugging */
-	if (on_waitlist)
-		MyProc->lwWaiting = LW_WS_NOT_WAITING;
+	if (found)
+		MyProc->lwWaiting = false;
 	else
 	{
 		int			extraWaits = 0;
@@ -1092,7 +1089,7 @@ LWLockDequeueSelf(LWLock *lock)
 		for (;;)
 		{
 			PGSemaphoreLock(MyProc->sem);
-			if (MyProc->lwWaiting == LW_WS_NOT_WAITING)
+			if (!MyProc->lwWaiting)
 				break;
 			extraWaits++;
 		}
@@ -1242,7 +1239,7 @@ LWLockAcquire(LWLock *lock, LWLockMode mode)
 		for (;;)
 		{
 			PGSemaphoreLock(proc->sem);
-			if (proc->lwWaiting == LW_WS_NOT_WAITING)
+			if (!proc->lwWaiting)
 				break;
 			extraWaits++;
 		}
@@ -1402,7 +1399,7 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
 			for (;;)
 			{
 				PGSemaphoreLock(proc->sem);
-				if (proc->lwWaiting == LW_WS_NOT_WAITING)
+				if (!proc->lwWaiting)
 					break;
 				extraWaits++;
 			}
@@ -1614,7 +1611,7 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
 		for (;;)
 		{
 			PGSemaphoreLock(proc->sem);
-			if (proc->lwWaiting == LW_WS_NOT_WAITING)
+			if (!proc->lwWaiting)
 				break;
 			extraWaits++;
 		}
@@ -1693,10 +1690,6 @@ LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
 
 		proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
 		proclist_push_tail(&wakeup, iter.cur, lwWaitLink);
-
-		/* see LWLockWakeup() */
-		Assert(waiter->lwWaiting == LW_WS_WAITING);
-		waiter->lwWaiting = LW_WS_PENDING_WAKEUP;
 	}
 
 	/* We are done updating shared state of the lock itself. */
@@ -1712,7 +1705,7 @@ LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
 		proclist_delete(&wakeup, iter.cur, lwWaitLink);
 		/* check comment in LWLockWakeup() about this barrier */
 		pg_write_barrier();
-		waiter->lwWaiting = LW_WS_NOT_WAITING;
+		waiter->lwWaiting = false;
 		PGSemaphoreUnlock(waiter->sem);
 	}
 }

src/backend/storage/lmgr/proc.c

@@ -403,7 +403,7 @@ InitProcess(void)
 	/* NB -- autovac launcher intentionally does not set IS_AUTOVACUUM */
 	if (IsAutoVacuumWorkerProcess())
 		MyPgXact->vacuumFlags |= PROC_IS_AUTOVACUUM;
-	MyProc->lwWaiting = LW_WS_NOT_WAITING;
+	MyProc->lwWaiting = false;
 	MyProc->lwWaitMode = 0;
 	MyProc->waitLock = NULL;
 	MyProc->waitProcLock = NULL;
@@ -583,7 +583,7 @@ InitAuxiliaryProcess(void)
 	MyPgXact->delayChkpt = false;
 	MyProc->delayChkptEnd = false;
 	MyPgXact->vacuumFlags = 0;
-	MyProc->lwWaiting = LW_WS_NOT_WAITING;
+	MyProc->lwWaiting = false;
 	MyProc->lwWaitMode = 0;
 	MyProc->waitLock = NULL;
 	MyProc->waitProcLock = NULL;

src/include/storage/lwlock.h

@@ -24,14 +24,6 @@
 
 struct PGPROC;
 
-/* what state of the wait process is a backend in */
-typedef enum LWLockWaitState
-{
-	LW_WS_NOT_WAITING, /* not currently waiting / woken up */
-	LW_WS_WAITING, /* currently waiting */
-	LW_WS_PENDING_WAKEUP /* removed from waitlist, but not yet signalled */
-} LWLockWaitState;
-
 /*
  * Code outside of lwlock.c should not manipulate the contents of this
  * structure directly, but we have to declare it here to allow LWLocks to be

src/include/storage/proc.h

@@ -134,7 +134,7 @@ struct PGPROC
 	bool		recoveryConflictPending;
 
 	/* Info about LWLock the process is currently waiting for, if any. */
-	uint8		lwWaiting;		/* see LWLockWaitState */
+	bool		lwWaiting;		/* true if waiting for an LW lock */
 	uint8		lwWaitMode;		/* lwlock mode being waited for */
 	proclist_node lwWaitLink;	/* position in LW lock wait list */