Fix handling of backgroundworker->WalSender promotion

Additionally, deduplicate some bkendtype-adjusting code in
SignalChildren/CountChildren, unifying handling and reducing chances of bugs.

Author: Matthias van de Meent

src/backend/postmaster/pmchild.c

@@ -250,7 +250,20 @@ ReleasePostmasterChildSlot(PMChild *pmchild)
 
 		/* WAL senders start out as regular backends, and share the pool */
 		if (pmchild->bkend_type == B_WAL_SENDER)
+		{
 			pool = &pmchild_pools[B_BACKEND];
+
+			/*
+			 * NEON: The released slot may be from a BGWorker upgraded to a
+			 * WalSender, so make sure we release the child back to the right
+			 * pool.
+			 */
+			if (pmchild->pid < pool->first_slotno &&
+				pmchild->pid >= pool->first_slotno + pool->size)
+			{
+				pool = &pmchild_pools[B_BG_WORKER];
+			}
+		}
 		else
 			pool = &pmchild_pools[pmchild->bkend_type];
 

src/backend/postmaster/postmaster.c

@@ -3475,6 +3475,34 @@ signal_child(PMChild *pmchild, int signal)
 #endif
 }
 
+static void
+adjust_bkendtype_if_needed(PMChild *bp, BackendTypeMask targetMask)
+{
+	/*
+	 * If we need to distinguish between B_BACKEND and B_WAL_SENDER, check
+	 * if any B_BACKEND backends have recently announced that they are
+	 * actually WAL senders.
+	 */
+	if (btmask_contains(targetMask, B_WAL_SENDER) != btmask_contains(targetMask, B_BACKEND) &&
+		bp->bkend_type == B_BACKEND)
+	{
+		if (IsPostmasterChildWalSender(bp->child_slot))
+			bp->bkend_type = B_WAL_SENDER;
+	}
+
+	/*
+	 * If we need to distinguish between B_BG_WORKER and B_WAL_SENDER,
+	 * check if any B_BG_WORKER backends have recently announced that
+	 * they are actually WAL senders.
+	 */
+	if (btmask_contains(targetMask, B_WAL_SENDER) != btmask_contains(targetMask, B_BG_WORKER) &&
+		bp->bkend_type == B_BG_WORKER)
+	{
+		if (IsPostmasterChildWalSender(bp->child_slot))
+			bp->bkend_type = B_WAL_SENDER;
+	}
+}
+
 /*
  * Send a signal to the targeted children.
  */
@@ -3488,29 +3516,7 @@ SignalChildren(int signal, BackendTypeMask targetMask)
 	{
 		PMChild    *bp = dlist_container(PMChild, elem, iter.cur);
 
-		/*
-		 * If we need to distinguish between B_BACKEND and B_WAL_SENDER, check
-		 * if any B_BACKEND backends have recently announced that they are
-		 * actually WAL senders.
-		 */
-		if (btmask_contains(targetMask, B_WAL_SENDER) != btmask_contains(targetMask, B_BACKEND) &&
-			bp->bkend_type == B_BACKEND)
-		{
-			if (IsPostmasterChildWalSender(bp->child_slot))
-				bp->bkend_type = B_WAL_SENDER;
-		}
-
-		/*
-		 * If we need to distinguish between B_BG_WORKER and B_WAL_SENDER,
-		 * check if any B_BG_WORKER backends have recently announced that
-		 * they are actually WAL senders.
-		 */
-		if (btmask_contains(targetMask, B_WAL_SENDER) != btmask_contains(targetMask, B_BG_WORKER) &&
-			bp->bkend_type  == B_BG_WORKER)
-		{
-			if (IsPostmasterChildWalSender(bp->child_slot))
-				bp->bkend_type = B_WAL_SENDER;
-		}
+		adjust_bkendtype_if_needed(bp, targetMask);
 
 		if (!btmask_contains(targetMask, bp->bkend_type))
 			continue;
@@ -3934,29 +3940,7 @@ CountChildren(BackendTypeMask targetMask)
 	{
 		PMChild    *bp = dlist_container(PMChild, elem, iter.cur);
 
-		/*
-		 * If we need to distinguish between B_BACKEND and B_WAL_SENDER, check
-		 * if any B_BACKEND backends have recently announced that they are
-		 * actually WAL senders.
-		 */
-		if (btmask_contains(targetMask, B_WAL_SENDER) != btmask_contains(targetMask, B_BACKEND) &&
-			bp->bkend_type == B_BACKEND)
-		{
-			if (IsPostmasterChildWalSender(bp->child_slot))
-				bp->bkend_type = B_WAL_SENDER;
-		}
-
-		/*
-		 * If we need to distinguish between B_BG_WORKER and B_WAL_SENDER,
-		 * check if any B_BG_WORKER backends have recently announced that
-		 * they are actually WAL senders.
-		 */
-		if (btmask_contains(targetMask, B_WAL_SENDER) != btmask_contains(targetMask, B_BG_WORKER) &&
-			bp->bkend_type == B_BG_WORKER)
-		{
-			if (IsPostmasterChildWalSender(bp->child_slot))
-				bp->bkend_type = B_WAL_SENDER;
-		}
+		adjust_bkendtype_if_needed(bp, targetMask);
 
 		if (!btmask_contains(targetMask, bp->bkend_type))
 			continue;