From: Andres Freund <andres@anarazel.de>
Date: Wed, 1 Mar 2017 04:41:44 +0000 (-0800)
Subject: Fix assertion failure due to over-eager code deduplication.
X-Git-Tag: REL_10_BETA1~811
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=123ccbe58309d08e42009e99a4b34a3a1aef7798;p=postgresql

Fix assertion failure due to over-eager code deduplication.

In the previous commit I'd made MemoryContextContains() use
GetMemoryChunkContext(), but that causes trouble when the passed
pointer isn't allocated in any memory context - that's probably
something we shouldn't do, but the previous commit isn't a place for a
"policy" change.
---

diff --git a/src/backend/utils/mmgr/mcxt.c b/src/backend/utils/mmgr/mcxt.c
index 07732ba59b..6668bf135e 100644
--- a/src/backend/utils/mmgr/mcxt.c
+++ b/src/backend/utils/mmgr/mcxt.c
@@ -566,7 +566,24 @@ MemoryContextCheck(MemoryContext context)
 bool
 MemoryContextContains(MemoryContext context, void *pointer)
 {
-	MemoryContext ptr_context = GetMemoryChunkContext(pointer);
+	MemoryContext ptr_context;
+
+	/*
+	 * NB: Can't use GetMemoryChunkContext() here - that performs assertions
+	 * that aren't acceptable here since we might be passed memory not
+	 * allocated by any memory context.
+	 *
+	 * Try to detect bogus pointers handed to us, poorly though we can.
+	 * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an
+	 * allocated chunk.
+	 */
+	if (pointer == NULL || pointer != (void *) MAXALIGN(pointer))
+		return false;
+
+	/*
+	 * OK, it's probably safe to look at the context.
+	 */
+	ptr_context = *(MemoryContext *) (((char *) pointer) - sizeof(void *));
 
 	return ptr_context == context;
 }