v1-0002-Better-comments-and-variable-name-in-AllocSetReal.patch

From 7cdaee9caaf96564237e4cfa8279699a36942624 Mon Sep 17 00:00:00 2001
From: Karina Litskevich <litskevichkarina@gmail.com>
Date: Tue, 14 Feb 2023 17:18:30 +0300
Subject: [PATCH v1 2/2] Better comments and variable name in AllocSetRealloc()

---
 src/backend/utils/mmgr/aset.c | 46 ++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 19 deletions(-)

diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index 1ff0bb83cb..35007750a9 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -1112,7 +1112,7 @@ AllocSetRealloc(void *pointer, Size size)
 	AllocBlock	block;
 	AllocSet	set;
 	MemoryChunk *chunk = PointerGetMemoryChunk(pointer);
-	Size		oldsize;
+	Size		oldchksize;
 	int			fidx;
 
 	/* Allow access to private part of chunk header. */
@@ -1140,11 +1140,11 @@ AllocSetRealloc(void *pointer, Size size)
 
 		set = block->aset;
 
-		oldsize = block->endptr - (char *) pointer;
+		oldchksize = block->endptr - (char *) pointer;
 
 #ifdef MEMORY_CONTEXT_CHECKING
 		/* Test for someone scribbling on unused space in chunk */
-		Assert(chunk->requested_size < oldsize);
+		Assert(chunk->requested_size < oldchksize);
 		if (!sentinel_ok(pointer, chunk->requested_size))
 			elog(WARNING, "detected write past chunk end in %s %p",
 				 set->header.name, chunk);
@@ -1194,14 +1194,17 @@ AllocSetRealloc(void *pointer, Size size)
 #endif
 
 		/*
-		 * realloc() (or randomize_mem()) will have left any newly-allocated
-		 * part UNDEFINED, but we may need to adjust trailing bytes from the
-		 * old allocation.
+		 * If this is an increase, realloc() (or randomize_mem()) will have left
+		 * any newly-allocated part UNDEFINED, but we may need to adjust
+		 * trailing bytes from the old allocation as they are marked NOACCESS.
 		 */
 #ifdef USE_VALGRIND
-		if (size > chunk->requested_size && oldsize > chunk->requested_size)
+		if (size > chunk->requested_size && oldchksize > chunk->requested_size)
+		{
+			Assert(chksize >= oldchksize);
 			VALGRIND_MAKE_MEM_UNDEFINED((char *) pointer + chunk->requested_size,
-										oldsize - chunk->requested_size);
+										oldchksize - chunk->requested_size);
+		}
 #endif
 
 		chunk->requested_size = size;
@@ -1211,12 +1214,15 @@ AllocSetRealloc(void *pointer, Size size)
 #else							/* !MEMORY_CONTEXT_CHECKING */
 
 		/*
-		 * We don't know how much of the old chunk size was the actual
-		 * allocation; it could have been as small as one byte.  We have to be
-		 * conservative and just mark the entire old portion DEFINED.
+		 * We may need to adjust marking of bytes from the old allocation as
+		 * some of them may be marked NOACCESS.  We don't know how much of the
+		 * old chunk size was the requested size; it could have been as small as
+		 * one byte.  We have to be conservative and just mark the entire old
+		 * portion DEFINED.  Make sure not to mark memory behind the new
+		 * allocation in case it's smaller than old one.
 		 */
-		if (size >= oldsize)
-			VALGRIND_MAKE_MEM_DEFINED(pointer, oldsize);
+		if (size >= oldchksize)
+			VALGRIND_MAKE_MEM_DEFINED(pointer, oldchksize);
 		else
 			VALGRIND_MAKE_MEM_DEFINED(pointer, size);
 #endif
@@ -1243,11 +1249,11 @@ AllocSetRealloc(void *pointer, Size size)
 
 	fidx = MemoryChunkGetValue(chunk);
 	Assert(FreeListIdxIsValid(fidx));
-	oldsize = GetChunkSizeFromFreeListIdx(fidx);
+	oldchksize = GetChunkSizeFromFreeListIdx(fidx);
 
 #ifdef MEMORY_CONTEXT_CHECKING
 	/* Test for someone scribbling on unused space in chunk */
-	if (chunk->requested_size < oldsize)
+	if (chunk->requested_size < oldchksize)
 		if (!sentinel_ok(pointer, chunk->requested_size))
 			elog(WARNING, "detected write past chunk end in %s %p",
 				 set->header.name, chunk);
@@ -1258,7 +1264,7 @@ AllocSetRealloc(void *pointer, Size size)
 	 * allocated area already is >= the new size.  (In particular, we will
 	 * fall out here if the requested size is a decrease.)
 	 */
-	if (oldsize >= size)
+	if (oldchksize >= size)
 	{
 #ifdef MEMORY_CONTEXT_CHECKING
 		Size		oldrequest = chunk->requested_size;
@@ -1281,10 +1287,10 @@ AllocSetRealloc(void *pointer, Size size)
 										size - oldrequest);
 		else
 			VALGRIND_MAKE_MEM_NOACCESS((char *) pointer + size,
-									   oldsize - size);
+									   oldchksize - size);
 
 		/* set mark to catch clobber of "unused" space */
-		if (size < oldsize)
+		if (size < oldchksize)
 			set_sentinel(pointer, size);
 #else							/* !MEMORY_CONTEXT_CHECKING */
 
@@ -1293,7 +1299,7 @@ AllocSetRealloc(void *pointer, Size size)
 		 * the old request or shrinking it, so we conservatively mark the
 		 * entire new allocation DEFINED.
 		 */
-		VALGRIND_MAKE_MEM_NOACCESS(pointer, oldsize);
+		VALGRIND_MAKE_MEM_NOACCESS(pointer, oldchksize);
 		VALGRIND_MAKE_MEM_DEFINED(pointer, size);
 #endif
 
@@ -1316,6 +1322,7 @@ AllocSetRealloc(void *pointer, Size size)
 		 * memory indefinitely.  See pgsql-hackers archives for 2007-08-11.)
 		 */
 		AllocPointer newPointer;
+		Size		 oldsize;
 
 		/* allocate new chunk */
 		newPointer = AllocSetAlloc((MemoryContext) set, size);
@@ -1340,6 +1347,7 @@ AllocSetRealloc(void *pointer, Size size)
 #ifdef MEMORY_CONTEXT_CHECKING
 		oldsize = chunk->requested_size;
 #else
+		oldsize = oldchksize;
 		VALGRIND_MAKE_MEM_DEFINED(pointer, oldsize);
 #endif
 
-- 
2.25.1