From 2c21d4d24e9eecdc728d6daabf499927b674a2eb Mon Sep 17 00:00:00 2001
From: Sergey Sargsyan <78570620+Serge-sudo@users.noreply.github.com>
Date: Thu, 19 Mar 2026 15:01:04 +0000
Subject: [PATCH] Fix loss of root/meta blkno after self-invalidation; defer
 invalidation processing under page locks

Fix an issue where B-tree descriptor state (`metaPageBlkno` and `rootPageBlkno`) could be lost after processing an invalidation message within the same transaction.

Previously, after `o_btree_load_shmem()` initialized the descriptor, a invalidation message could be processed before the descriptor was used. This caused the descriptor to be recreated, resetting `metaPageBlkno` and `rootPageBlkno` to `InvalidBlockNumber`, which led to assertion failures (e.g. in `btree_ctid_get_and_inc`).

While investigating, another problem was identified: invalidation message processing may occur while holding page locks. Invalidation handlers access system trees, and if required pages are evicted, they trigger page loads. This leads to `load_page()` being called while locks are held, hitting assertions that forbid holding locks during page load.

To address both issues:

* Ensure descriptor state is not lost due to mid-operation self-invalidation
* Introduce deferred invalidation handling:

  * Skip invalidation message processing when it is unsafe (e.g. while holding page locks)
  * Process pending invalidation messages at the next safe point

This prevents descriptor corruption and avoids unsafe page loads under locks.
---
 src/backend/utils/cache/inval.c | 18 ++++++++++++++++++
 src/include/utils/inval.h       |  5 +++++
 2 files changed, 23 insertions(+)

diff --git a/src/backend/utils/cache/inval.c b/src/backend/utils/cache/inval.c
index f5775880416..4fbca7b5711 100644
--- a/src/backend/utils/cache/inval.c
+++ b/src/backend/utils/cache/inval.c
@@ -240,6 +240,9 @@ static TransInvalidationInfo *transInvalInfo = NULL;
 /* GUC storage */
 int			debug_discard_caches = 0;
 
+/* Hook for extensions to receive custom invalidation messages */
+ReceiveCustomInvalMessage_hook_type ReceiveCustomInvalMessage_hook = NULL;
+
 /*
  * Dynamically-registered callback functions.  Current implementation
  * assumes there won't be enough of these to justify a dynamically resizable
@@ -827,6 +830,18 @@ InvalidateSystemCaches(void)
 	InvalidateSystemCachesExtended(false);
 }
 
+/*
+ * ReceiveCustomInvalMessage
+ *		Call the ReceiveCustomInvalMessage_hook if set, allowing extensions
+ *		to process their own invalidation messages.
+ */
+void
+ReceiveCustomInvalMessage(void)
+{
+	if (ReceiveCustomInvalMessage_hook)
+		(*ReceiveCustomInvalMessage_hook) ();
+}
+
 /*
  * AcceptInvalidationMessages
  *		Read and process invalidation messages from the shared invalidation
@@ -838,6 +853,9 @@ InvalidateSystemCaches(void)
 void
 AcceptInvalidationMessages(void)
 {
+	/* Process any messages from external sources first. */
+	ReceiveCustomInvalMessage();
+
 	ReceiveSharedInvalidMessages(LocalExecuteInvalidationMessage,
 								 InvalidateSystemCaches);
 
diff --git a/src/include/utils/inval.h b/src/include/utils/inval.h
index 69498b9f77f..1ab129f9376 100644
--- a/src/include/utils/inval.h
+++ b/src/include/utils/inval.h
@@ -20,12 +20,17 @@
 
 extern PGDLLIMPORT int debug_discard_caches;
 
+/* Hook for extensions to receive custom invalidation messages */
+typedef void (*ReceiveCustomInvalMessage_hook_type) (void);
+extern PGDLLIMPORT ReceiveCustomInvalMessage_hook_type ReceiveCustomInvalMessage_hook;
+
 typedef void (*SyscacheCallbackFunction) (Datum arg, int cacheid, uint32 hashvalue);
 typedef void (*RelcacheCallbackFunction) (Datum arg, Oid relid);
 typedef void (*UsercacheCallbackFunction) (Datum arg, Oid arg1, Oid arg2, Oid arg3);
 
 
 extern void AcceptInvalidationMessages(void);
+extern void ReceiveCustomInvalMessage(void);
 
 extern void AtEOXact_Inval(bool isCommit);