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From: Chao Li <[email protected]>
To: PostgreSQL mailing lists <[email protected]>
Subject: pg_upgrade: fix memory leak in SLRU I/O code
Date: Wed, 4 Feb 2026 17:20:49 +0800
Message-ID: <[email protected]> (raw)

Hi Hackers,

This comes from a previous review and has been on my to-do list for a while.

Since src/bin/pg_upgrade/slru_io.c includes postgres_fe.h, it is frontend code, so backend memory contexts are not used here.

In the current code:
```
void
FreeSlruWrite(SlruSegState *state)
{
	Assert(state->writing);

	SlruFlush(state);

	if (state->fd != -1)
		close(state->fd);
	pg_free(state);
}
```

the SlruSegState itself is freed, but state->dir and state->fn are not, which results in a memory leak during pg_upgrade runs. More generally, I don’t see a reason to free an object itself without also freeing the memory owned by its members.

While looking at this, I also noticed that state->dir is allocated using pstrdup(). To better align with frontend conventions, the patch switches this to pg_strdup() and introduces a common cleanup helper to free all resources associated with SlruSegState.

See the attached patch.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/






Attachments:

  [application/octet-stream] v1-0001-pg_upgrade-fix-memory-leak-in-SLRU-I-O-code.patch (2.0K, ../[email protected]/2-v1-0001-pg_upgrade-fix-memory-leak-in-SLRU-I-O-code.patch)
  download | inline diff:
From f06d718e119cbf17ac9a7aecb41eed385a4f4f41 Mon Sep 17 00:00:00 2001
From: "Chao Li (Evan)" <[email protected]>
Date: Wed, 4 Feb 2026 16:53:00 +0800
Subject: [PATCH v1] pg_upgrade: fix memory leak in SLRU I/O code

SlruSegState->dir is allocated in AllocSlruSegState() but was never freed.
Add a common cleanup helper to release all resources associated with an
SLRU segment state and use it for both readers and writers.

Author: Chao Li <[email protected]>
Reviewed-by:
Discussion: https://postgr.es/m/
---
 src/bin/pg_upgrade/slru_io.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/bin/pg_upgrade/slru_io.c b/src/bin/pg_upgrade/slru_io.c
index ae3e224d7b1..efc0fb71dda 100644
--- a/src/bin/pg_upgrade/slru_io.c
+++ b/src/bin/pg_upgrade/slru_io.c
@@ -19,6 +19,7 @@
 #include "slru_io.h"
 
 static SlruSegState *AllocSlruSegState(const char *dir);
+static void FreeSlruSegState(SlruSegState *state);
 static char *SlruFileName(SlruSegState *state, int64 segno);
 static void SlruFlush(SlruSegState *state);
 
@@ -28,7 +29,7 @@ AllocSlruSegState(const char *dir)
 {
 	SlruSegState *state = pg_malloc(sizeof(*state));
 
-	state->dir = pstrdup(dir);
+	state->dir = pg_strdup(dir);
 	state->fn = NULL;
 	state->fd = -1;
 	state->segno = -1;
@@ -69,6 +70,17 @@ AllocSlruRead(const char *dir, bool long_segment_names)
 	return state;
 }
 
+static void
+FreeSlruSegState(SlruSegState *state)
+{
+	if (state->fd != -1)
+		close(state->fd);
+
+	pg_free(state->fn);
+	pg_free(state->dir);
+	pg_free(state);
+}
+
 /*
  * Read the given page into memory buffer.
  *
@@ -154,9 +166,7 @@ FreeSlruRead(SlruSegState *state)
 {
 	Assert(!state->writing);	/* read only mode */
 
-	if (state->fd != -1)
-		close(state->fd);
-	pg_free(state);
+	FreeSlruSegState(state);
 }
 
 /*
@@ -263,7 +273,5 @@ FreeSlruWrite(SlruSegState *state)
 
 	SlruFlush(state);
 
-	if (state->fd != -1)
-		close(state->fd);
-	pg_free(state);
+	FreeSlruSegState(state);
 }
-- 
2.50.1 (Apple Git-155)

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