From 01f0be03b55e97fd3d1679e25415e1474513419e Mon Sep 17 00:00:00 2001
From: Konstantin Knizhnik <knizhnik@garret.ru>
Date: Thu, 6 Feb 2025 09:00:00 +0200
Subject: [PATCH] Fix bugs in lfc_cache_containsv (#10682)

## Problem

Incorrect manipulations with iteration index in `lfc_cache_containsv`

## Summary of changes

```
-		int		this_chunk = Min(nblocks, BLOCKS_PER_CHUNK - chunk_offs);
+		int		this_chunk = Min(nblocks - i, BLOCKS_PER_CHUNK - chunk_offs);		int		this_chunk = ```
 -		if (i + 1 >= nblocks)
+		if (i >= nblocks)
```

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
---
 pgxn/neon/file_cache.c | 39 ++++++++++++++++++---------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/pgxn/neon/file_cache.c b/pgxn/neon/file_cache.c
index 01da61f84b..a61dc9f4c6 100644
--- a/pgxn/neon/file_cache.c
+++ b/pgxn/neon/file_cache.c
@@ -509,47 +509,44 @@ lfc_cache_containsv(NRelFileInfo rinfo, ForkNumber forkNum, BlockNumber blkno,
 
 	CriticalAssert(BufTagGetRelNumber(&tag) != InvalidRelFileNumber);
 
-	tag.blockNum = (blkno + i) & ~(BLOCKS_PER_CHUNK - 1);
+	tag.blockNum = blkno & ~(BLOCKS_PER_CHUNK - 1);
 	hash = get_hash_value(lfc_hash, &tag);
-	chunk_offs = (blkno + i) & (BLOCKS_PER_CHUNK - 1);
+	chunk_offs = blkno & (BLOCKS_PER_CHUNK - 1);
 
 	LWLockAcquire(lfc_lock, LW_SHARED);
 
+	if (!LFC_ENABLED())
+	{
+		LWLockRelease(lfc_lock);
+		return 0;
+	}
 	while (true)
 	{
-		int		this_chunk = Min(nblocks, BLOCKS_PER_CHUNK - chunk_offs);
-		if (LFC_ENABLED())
-		{
-			entry = hash_search_with_hash_value(lfc_hash, &tag, hash, HASH_FIND, NULL);
+		int		this_chunk = Min(nblocks - i, BLOCKS_PER_CHUNK - chunk_offs);
+		entry = hash_search_with_hash_value(lfc_hash, &tag, hash, HASH_FIND, NULL);
 
-			if (entry != NULL)
+		if (entry != NULL)
+		{
+			for (; chunk_offs < BLOCKS_PER_CHUNK && i < nblocks; chunk_offs++, i++)
 			{
-				for (; chunk_offs < BLOCKS_PER_CHUNK && i < nblocks; chunk_offs++, i++)
+				if ((entry->bitmap[chunk_offs >> 5] & 
+					 ((uint32)1 << (chunk_offs & 31))) != 0)
 				{
-					if ((entry->bitmap[chunk_offs >> 5] & 
-						((uint32)1 << (chunk_offs & 31))) != 0)
-					{
-						BITMAP_SET(bitmap, i);
-						found++;
-					}
+					BITMAP_SET(bitmap, i);
+					found++;
 				}
 			}
-			else
-			{
-				i += this_chunk;
-			}
 		}
 		else
 		{
-			LWLockRelease(lfc_lock);
-			return found;
+			i += this_chunk;
 		}
 
 		/*
 		 * Break out of the iteration before doing expensive stuff for
 		 * a next iteration
 		 */
-		if (i + 1 >= nblocks)
+		if (i >= nblocks)
 			break;
 
 		/*