v3-0001-Add-macros-for-safety-access-to-smgr.patch

From a1c572652e69f13b954ec3a915ed55c1ec11c772 Mon Sep 17 00:00:00 2001
From: Daniil Davidov <d.davydov@postgrespro.ru>
Date: Mon, 14 Apr 2025 13:07:38 +0700
Subject: [PATCH v3] Add macros for safety access to smgr

---
 src/backend/storage/buffer/bufmgr.c   | 55 ++++++++++++---------------
 src/backend/storage/buffer/localbuf.c |  9 +++--
 src/include/storage/bufmgr.h          | 13 +++++++
 3 files changed, 43 insertions(+), 34 deletions(-)

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 0b0e056eea2..f2b117088a8 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -892,11 +892,8 @@ ExtendBufferedRelBy(BufferManagerRelation bmr,
 	Assert(bmr.smgr == NULL || bmr.relpersistence != 0);
 	Assert(extend_by > 0);
 
-	if (bmr.smgr == NULL)
-	{
-		bmr.smgr = RelationGetSmgr(bmr.rel);
+	if (bmr.relpersistence == 0)
 		bmr.relpersistence = bmr.rel->rd_rel->relpersistence;
-	}
 
 	return ExtendBufferedRelCommon(bmr, fork, strategy, flags,
 								   extend_by, InvalidBlockNumber,
@@ -928,11 +925,8 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
 	Assert(bmr.smgr == NULL || bmr.relpersistence != 0);
 	Assert(extend_to != InvalidBlockNumber && extend_to > 0);
 
-	if (bmr.smgr == NULL)
-	{
-		bmr.smgr = RelationGetSmgr(bmr.rel);
+	if (bmr.relpersistence == 0)
 		bmr.relpersistence = bmr.rel->rd_rel->relpersistence;
-	}
 
 	/*
 	 * If desired, create the file if it doesn't exist.  If
@@ -940,15 +934,15 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
 	 * an smgrexists call.
 	 */
 	if ((flags & EB_CREATE_FORK_IF_NEEDED) &&
-		(bmr.smgr->smgr_cached_nblocks[fork] == 0 ||
-		 bmr.smgr->smgr_cached_nblocks[fork] == InvalidBlockNumber) &&
-		!smgrexists(bmr.smgr, fork))
+		(BMR_GET_SMGR(bmr)->smgr_cached_nblocks[fork] == 0 ||
+		 BMR_GET_SMGR(bmr)->smgr_cached_nblocks[fork] == InvalidBlockNumber) &&
+		!smgrexists(BMR_GET_SMGR(bmr), fork))
 	{
 		LockRelationForExtension(bmr.rel, ExclusiveLock);
 
 		/* recheck, fork might have been created concurrently */
-		if (!smgrexists(bmr.smgr, fork))
-			smgrcreate(bmr.smgr, fork, flags & EB_PERFORMING_RECOVERY);
+		if (!smgrexists(BMR_GET_SMGR(bmr), fork))
+			smgrcreate(BMR_GET_SMGR(bmr), fork, flags & EB_PERFORMING_RECOVERY);
 
 		UnlockRelationForExtension(bmr.rel, ExclusiveLock);
 	}
@@ -958,13 +952,13 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
 	 * kernel.
 	 */
 	if (flags & EB_CLEAR_SIZE_CACHE)
-		bmr.smgr->smgr_cached_nblocks[fork] = InvalidBlockNumber;
+		BMR_GET_SMGR(bmr)->smgr_cached_nblocks[fork] = InvalidBlockNumber;
 
 	/*
 	 * Estimate how many pages we'll need to extend by. This avoids acquiring
 	 * unnecessarily many victim buffers.
 	 */
-	current_size = smgrnblocks(bmr.smgr, fork);
+	current_size = smgrnblocks(BMR_GET_SMGR(bmr), fork);
 
 	/*
 	 * Since no-one else can be looking at the page contents yet, there is no
@@ -1008,7 +1002,7 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
 	if (buffer == InvalidBuffer)
 	{
 		Assert(extended_by == 0);
-		buffer = ReadBuffer_common(bmr.rel, bmr.smgr, bmr.relpersistence,
+		buffer = ReadBuffer_common(bmr.rel, BMR_GET_SMGR(bmr), bmr.relpersistence,
 								   fork, extend_to - 1, mode, strategy);
 	}
 
@@ -2568,10 +2562,10 @@ ExtendBufferedRelCommon(BufferManagerRelation bmr,
 	BlockNumber first_block;
 
 	TRACE_POSTGRESQL_BUFFER_EXTEND_START(fork,
-										 bmr.smgr->smgr_rlocator.locator.spcOid,
-										 bmr.smgr->smgr_rlocator.locator.dbOid,
-										 bmr.smgr->smgr_rlocator.locator.relNumber,
-										 bmr.smgr->smgr_rlocator.backend,
+										 BMR_GET_SMGR(bmr)->smgr_rlocator.locator.spcOid,
+										 BMR_GET_SMGR(bmr)->smgr_rlocator.locator.dbOid,
+										 BMR_GET_SMGR(bmr)->smgr_rlocator.locator.relNumber,
+										 BMR_GET_SMGR(bmr)->smgr_rlocator.backend,
 										 extend_by);
 
 	if (bmr.relpersistence == RELPERSISTENCE_TEMP)
@@ -2585,10 +2579,10 @@ ExtendBufferedRelCommon(BufferManagerRelation bmr,
 	*extended_by = extend_by;
 
 	TRACE_POSTGRESQL_BUFFER_EXTEND_DONE(fork,
-										bmr.smgr->smgr_rlocator.locator.spcOid,
-										bmr.smgr->smgr_rlocator.locator.dbOid,
-										bmr.smgr->smgr_rlocator.locator.relNumber,
-										bmr.smgr->smgr_rlocator.backend,
+										BMR_GET_SMGR(bmr)->smgr_rlocator.locator.spcOid,
+										BMR_GET_SMGR(bmr)->smgr_rlocator.locator.dbOid,
+										BMR_GET_SMGR(bmr)->smgr_rlocator.locator.relNumber,
+										BMR_GET_SMGR(bmr)->smgr_rlocator.backend,
 										*extended_by,
 										first_block);
 
@@ -2654,9 +2648,9 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 	 * kernel.
 	 */
 	if (flags & EB_CLEAR_SIZE_CACHE)
-		bmr.smgr->smgr_cached_nblocks[fork] = InvalidBlockNumber;
+		BMR_GET_SMGR(bmr)->smgr_cached_nblocks[fork] = InvalidBlockNumber;
 
-	first_block = smgrnblocks(bmr.smgr, fork);
+	first_block = smgrnblocks(BMR_GET_SMGR(bmr), fork);
 
 	/*
 	 * Now that we have the accurate relation size, check if the caller wants
@@ -2699,7 +2693,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 		ereport(ERROR,
 				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 				 errmsg("cannot extend relation %s beyond %u blocks",
-						relpath(bmr.smgr->smgr_rlocator, fork).str,
+						relpath(BMR_GET_SMGR(bmr)->smgr_rlocator, fork).str,
 						MaxBlockNumber)));
 
 	/*
@@ -2721,7 +2715,8 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 		ResourceOwnerEnlarge(CurrentResourceOwner);
 		ReservePrivateRefCountEntry();
 
-		InitBufferTag(&tag, &bmr.smgr->smgr_rlocator.locator, fork, first_block + i);
+		InitBufferTag(&tag, &BMR_GET_SMGR(bmr)->smgr_rlocator.locator, fork,
+					  first_block + i);
 		hash = BufTableHashCode(&tag);
 		partition_lock = BufMappingPartitionLock(hash);
 
@@ -2771,7 +2766,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 				ereport(ERROR,
 						(errmsg("unexpected data beyond EOF in block %u of relation %s",
 								existing_hdr->tag.blockNum,
-								relpath(bmr.smgr->smgr_rlocator, fork).str),
+								relpath(BMR_GET_SMGR(bmr)->smgr_rlocator, fork).str),
 						 errhint("This has been seen to occur with buggy kernels; consider updating your system.")));
 
 			/*
@@ -2829,7 +2824,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 	 *
 	 * We don't need to set checksum for all-zero pages.
 	 */
-	smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
+	smgrzeroextend(BMR_GET_SMGR(bmr), fork, first_block, extend_by, false);
 
 	/*
 	 * Release the file-extension lock; it's now OK for someone else to extend
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 63101d56a07..a3bcc4e22b3 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -372,7 +372,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 		MemSet(buf_block, 0, BLCKSZ);
 	}
 
-	first_block = smgrnblocks(bmr.smgr, fork);
+	first_block = smgrnblocks(BMR_GET_SMGR(bmr), fork);
 
 	if (extend_upto != InvalidBlockNumber)
 	{
@@ -391,7 +391,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 		ereport(ERROR,
 				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 				 errmsg("cannot extend relation %s beyond %u blocks",
-						relpath(bmr.smgr->smgr_rlocator, fork).str,
+						relpath(BMR_GET_SMGR(bmr)->smgr_rlocator, fork).str,
 						MaxBlockNumber)));
 
 	for (uint32 i = 0; i < extend_by; i++)
@@ -408,7 +408,8 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 		/* in case we need to pin an existing buffer below */
 		ResourceOwnerEnlarge(CurrentResourceOwner);
 
-		InitBufferTag(&tag, &bmr.smgr->smgr_rlocator.locator, fork, first_block + i);
+		InitBufferTag(&tag, &BMR_GET_SMGR(bmr)->smgr_rlocator.locator, fork,
+					  first_block + i);
 
 		hresult = (LocalBufferLookupEnt *)
 			hash_search(LocalBufHash, &tag, HASH_ENTER, &found);
@@ -456,7 +457,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/* actually extend relation */
-	smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
+	smgrzeroextend(BMR_GET_SMGR(bmr), fork, first_block, extend_by, false);
 
 	pgstat_count_io_op_time(IOOBJECT_TEMP_RELATION, IOCONTEXT_NORMAL, IOOP_EXTEND,
 							io_start, 1, extend_by * BLCKSZ);
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 33a8b8c06fb..880cb09a7a4 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -101,13 +101,26 @@ typedef enum ExtendBufferedFlags
 typedef struct BufferManagerRelation
 {
 	Relation	rel;
+
+	/*
+	 * Must be accessed via BMR_GET_SMGR if we want to access some fields
+	 * of structure
+	 */
 	struct SMgrRelationData *smgr;
+
 	char		relpersistence;
 } BufferManagerRelation;
 
 #define BMR_REL(p_rel) ((BufferManagerRelation){.rel = p_rel})
 #define BMR_SMGR(p_smgr, p_relpersistence) ((BufferManagerRelation){.smgr = p_smgr, .relpersistence = p_relpersistence})
 
+/*
+ * In case of cache invalidation, we need to be sure that we access a valid
+ * smgr reference
+ */
+#define BMR_GET_SMGR(bmr) \
+	(RelationIsValid((bmr).rel) ? RelationGetSmgr((bmr).rel) : (bmr).smgr)
+
 /* Zero out page if reading fails. */
 #define READ_BUFFERS_ZERO_ON_ERROR (1 << 0)
 /* Call smgrprefetch() if I/O necessary. */
-- 
2.43.0