Add more guards for prefetch_pump_state (#11859)

## Problem

See https://neondb.slack.com/archives/C08PJ07BZ44/p1746566292750689

Looks like there are more cases when `prefetch_pump_state` can be called
in unexpected place and cause core dump.

## Summary of changes

Add more guards.

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>

pgxn/neon/communicator.c

@@ -425,15 +425,12 @@ compact_prefetch_buffers(void)
  * point inside and outside PostgreSQL.
  *
  * This still does throw errors when it receives malformed responses from PS.
- *
- * When we're not called from CHECK_FOR_INTERRUPTS (indicated by
- * IsHandlingInterrupts) we also report we've ended prefetch receive work,
- * just in case state tracking was lost due to an error in the sync getPage
- * response code.
  */
 void
-communicator_prefetch_pump_state(bool IsHandlingInterrupts)
+communicator_prefetch_pump_state(void)
 {
+	START_PREFETCH_RECEIVE_WORK();
+
 	while (MyPState->ring_receive != MyPState->ring_flush)
 	{
 		NeonResponse   *response;
@@ -482,9 +479,7 @@ communicator_prefetch_pump_state(bool IsHandlingInterrupts)
 		}
 	}
 
-	/* We never pump the prefetch state while handling other pages */
-	if (!IsHandlingInterrupts)
-		END_PREFETCH_RECEIVE_WORK();
+	END_PREFETCH_RECEIVE_WORK();
 
 	communicator_reconfigure_timeout_if_needed();
 }
@@ -672,9 +667,10 @@ prefetch_wait_for(uint64 ring_index)
 
 	Assert(MyPState->ring_unused > ring_index);
 
+	START_PREFETCH_RECEIVE_WORK();
+
 	while (MyPState->ring_receive <= ring_index)
 	{
-		START_PREFETCH_RECEIVE_WORK();
 		entry = GetPrfSlot(MyPState->ring_receive);
 
 		Assert(entry->status == PRFS_REQUESTED);
@@ -683,17 +679,18 @@ prefetch_wait_for(uint64 ring_index)
 			result = false;
 			break;
 		}
-
-		END_PREFETCH_RECEIVE_WORK();
 		CHECK_FOR_INTERRUPTS();
 	}
+
 	if (result)
 	{
 		/* Check that slot is actually received (srver can be disconnected in prefetch_pump_state called from CHECK_FOR_INTERRUPTS */
 		PrefetchRequest *slot = GetPrfSlot(ring_index);
-		return slot->status == PRFS_RECEIVED;
+		result = slot->status == PRFS_RECEIVED;
 	}
-	return false;
+	END_PREFETCH_RECEIVE_WORK();
+
+	return result;
 ;
 }
 
@@ -720,6 +717,7 @@ prefetch_read(PrefetchRequest *slot)
 	Assert(slot->status == PRFS_REQUESTED);
 	Assert(slot->response == NULL);
 	Assert(slot->my_ring_index == MyPState->ring_receive);
+	Assert(readpage_reentrant_guard);
 
 	if (slot->status != PRFS_REQUESTED ||
 		slot->response != NULL ||
@@ -802,6 +800,7 @@ communicator_prefetch_receive(BufferTag tag)
 	PrfHashEntry *entry;
 	PrefetchRequest hashkey;
 
+	Assert(readpage_reentrant_guard);
 	hashkey.buftag = tag;
 	entry = prfh_lookup(MyPState->prf_hash, &hashkey);
 	if (entry != NULL && prefetch_wait_for(entry->slot->my_ring_index))
@@ -821,8 +820,12 @@ communicator_prefetch_receive(BufferTag tag)
 void
 prefetch_on_ps_disconnect(void)
 {
+	bool save_readpage_reentrant_guard = readpage_reentrant_guard;
 	MyPState->ring_flush = MyPState->ring_unused;
 
+	/* Prohibit callig of prefetch_pump_state */
+	START_PREFETCH_RECEIVE_WORK();
+
 	while (MyPState->ring_receive < MyPState->ring_unused)
 	{
 		PrefetchRequest *slot;
@@ -851,6 +854,9 @@ prefetch_on_ps_disconnect(void)
 		MyNeonCounters->getpage_prefetch_discards_total += 1;
 	}
 
+	/* Restore guard */
+	readpage_reentrant_guard = save_readpage_reentrant_guard;
+
 	/*
 	 * We can have gone into retry due to network error, so update stats with
 	 * the latest available
@@ -2509,7 +2515,7 @@ communicator_processinterrupts(void)
 	if (timeout_signaled)
 	{
 		if (!readpage_reentrant_guard && readahead_getpage_pull_timeout_ms > 0)
-			communicator_prefetch_pump_state(true);
+			communicator_prefetch_pump_state();
 
 		timeout_signaled = false;
 		communicator_reconfigure_timeout_if_needed();

pgxn/neon/communicator.h

@@ -44,7 +44,7 @@ extern int communicator_read_slru_segment(SlruKind kind, int64 segno,
 										  void *buffer);
 
 extern void communicator_reconfigure_timeout_if_needed(void);
-extern void communicator_prefetch_pump_state(bool IsHandlingInterrupts);
+extern void communicator_prefetch_pump_state(void);
 
 
 #endif

pgxn/neon/pagestore_smgr.c

@@ -1179,7 +1179,7 @@ neon_prefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 		blocknum += iterblocks;
 	}
 
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 	return false;
 }
@@ -1218,7 +1218,7 @@ neon_prefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum)
 
 	communicator_prefetch_register_bufferv(tag, NULL, 1, NULL);
 
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 	return false;
 }
@@ -1262,7 +1262,7 @@ neon_writeback(SMgrRelation reln, ForkNumber forknum,
 	 */
 	neon_log(SmgrTrace, "writeback noop");
 
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 #ifdef DEBUG_COMPARE_LOCAL
 	if (IS_LOCAL_REL(reln))
@@ -1315,7 +1315,7 @@ neon_read(SMgrRelation reln, ForkNumber forkNum, BlockNumber blkno, void *buffer
 	}
 
 	/* Try to read PS results if they are available */
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 	neon_get_request_lsns(InfoFromSMgrRel(reln), forkNum, blkno, &request_lsns, 1);
 
@@ -1339,7 +1339,7 @@ neon_read(SMgrRelation reln, ForkNumber forkNum, BlockNumber blkno, void *buffer
 	/*
 	 * Try to receive prefetch results once again just to make sure we don't leave the smgr code while the OS might still have buffered bytes.
 	 */
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 #ifdef DEBUG_COMPARE_LOCAL
 	if (forkNum == MAIN_FORKNUM && IS_LOCAL_REL(reln))
@@ -1449,7 +1449,7 @@ neon_readv(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 				 nblocks, PG_IOV_MAX);
 
 	/* Try to read PS results if they are available */
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 	neon_get_request_lsns(InfoFromSMgrRel(reln), forknum, blocknum,
 						  request_lsns, nblocks);
@@ -1480,7 +1480,7 @@ neon_readv(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 	/*
 	 * Try to receive prefetch results once again just to make sure we don't leave the smgr code while the OS might still have buffered bytes.
 	 */
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 #ifdef DEBUG_COMPARE_LOCAL
 	if (forknum == MAIN_FORKNUM && IS_LOCAL_REL(reln))
@@ -1665,7 +1665,7 @@ neon_write(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, const vo
 
 	lfc_write(InfoFromSMgrRel(reln), forknum, blocknum, buffer);
 
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 #ifdef DEBUG_COMPARE_LOCAL
 	if (IS_LOCAL_REL(reln))
@@ -1727,7 +1727,7 @@ neon_writev(SMgrRelation reln, ForkNumber forknum, BlockNumber blkno,
 
 	lfc_writev(InfoFromSMgrRel(reln), forknum, blkno, buffers, nblocks);
 
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 #ifdef DEBUG_COMPARE_LOCAL
 	if (IS_LOCAL_REL(reln))
@@ -1902,7 +1902,7 @@ neon_immedsync(SMgrRelation reln, ForkNumber forknum)
 
 	neon_log(SmgrTrace, "[NEON_SMGR] immedsync noop");
 
-	communicator_prefetch_pump_state(false);
+	communicator_prefetch_pump_state();
 
 #ifdef DEBUG_COMPARE_LOCAL
 	if (IS_LOCAL_REL(reln))

vendor/revisions.json

@@ -5,7 +5,7 @@
   ],
   "v16": [
     "16.8",
-    "05ddf212e2e07b788b5c8b88bdcf98630941f6ae"
+    "d72d76f2cdee4194dd052ce099e9784aca7c794a"
   ],
   "v15": [
     "15.12",