v1-0001-Add-guard-to-prevent-recursive-memory-contexts-lo.patch

From 5a65280d10fec6e4c5577e26eeddeb10c9ddb13f Mon Sep 17 00:00:00 2001
From: Fujii Masao <fujii@postgresql.org>
Date: Fri, 2 May 2025 00:35:48 +0900
Subject: [PATCH v1] Add guard to prevent recursive memory contexts logging.
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Previously, if memory contexts logging was triggered repeatedly and
rapidly while a previous request was still being processed, it could
result in recursive calls to ProcessLogMemoryContextInterrupt().
This could lead to infinite recursion and potentially crash the process.

This commit adds a guard to prevent such recursion.
If ProcessLogMemoryContextInterrupt() is already in progress and
logging memory contexts, subsequent calls will exit immediately,
avoiding unintended recursive calls.

While this scenario is unlikely in practice, it’s not impossible.
This change adds a safety check to prevent such failures.

Back-patch to v14, where memory contexts logging was introduced.
---
 src/backend/utils/mmgr/mcxt.c | 61 +++++++++++++++++++++++------------
 1 file changed, 41 insertions(+), 20 deletions(-)

diff --git a/src/backend/utils/mmgr/mcxt.c b/src/backend/utils/mmgr/mcxt.c
index 7d28ca706eb..907c7f7affe 100644
--- a/src/backend/utils/mmgr/mcxt.c
+++ b/src/backend/utils/mmgr/mcxt.c
@@ -1383,29 +1383,50 @@ HandleGetMemoryContextInterrupt(void)
 void
 ProcessLogMemoryContextInterrupt(void)
 {
+	static bool in_progress = false;
+
 	LogMemoryContextPending = false;
 
-	/*
-	 * Use LOG_SERVER_ONLY to prevent this message from being sent to the
-	 * connected client.
-	 */
-	ereport(LOG_SERVER_ONLY,
-			(errhidestmt(true),
-			 errhidecontext(true),
-			 errmsg("logging memory contexts of PID %d", MyProcPid)));
+	PG_TRY();
+	{
+		/*
+		 * Exit immediately if memory contexts logging is already in progress.
+		 * This prevents recursive calls, which could occur if logging is
+		 * requested  repeatedly and rapidly, potentially leading to infinite
+		 * recursion and a crash.
+		 */
+		if (in_progress)
+			return;
+		in_progress = true;
 
-	/*
-	 * When a backend process is consuming huge memory, logging all its memory
-	 * contexts might overrun available disk space. To prevent this, we limit
-	 * the depth of the hierarchy, as well as the number of child contexts to
-	 * log per parent to 100.
-	 *
-	 * As with MemoryContextStats(), we suppose that practical cases where the
-	 * dump gets long will typically be huge numbers of siblings under the
-	 * same parent context; while the additional debugging value from seeing
-	 * details about individual siblings beyond 100 will not be large.
-	 */
-	MemoryContextStatsDetail(TopMemoryContext, 100, 100, false);
+		/*
+		 * Use LOG_SERVER_ONLY to prevent this message from being sent to the
+		 * connected client.
+		 */
+		ereport(LOG_SERVER_ONLY,
+				(errhidestmt(true),
+				 errhidecontext(true),
+				 errmsg("logging memory contexts of PID %d", MyProcPid)));
+
+		/*
+		 * When a backend process is consuming huge memory, logging all its
+		 * memory contexts might overrun available disk space. To prevent
+		 * this, we limit the depth of the hierarchy, as well as the number of
+		 * child contexts to log per parent to 100.
+		 *
+		 * As with MemoryContextStats(), we suppose that practical cases where
+		 * the dump gets long will typically be huge numbers of siblings under
+		 * the same parent context; while the additional debugging value from
+		 * seeing details about individual siblings beyond 100 will not be
+		 * large.
+		 */
+		MemoryContextStatsDetail(TopMemoryContext, 100, 100, false);
+	}
+	PG_FINALLY();
+	{
+		in_progress = false;
+	}
+	PG_END_TRY();
 }
 
 /*
-- 
2.49.0