Subject: Re: pg_upgrade: fix memory leak in SLRU I/O code

From: Dilip Kumar <[email-masked]>
Date: Thu, 5 Feb 2026 09:32:49 +0530

On Wed, Feb 4, 2026 at 2:51 PM Chao Li <[email-masked]> wrote:
>
> 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.

The patch LGTM, just one suggestion, adds a one liner comment over the
new function[1] for consistency.

[1]
+static void
+FreeSlruSegState(SlruSegState *state)
+{
+ if (state->fd != -1)
+ close(state->fd);
+
+ pg_free(state->fn);
+ pg_free(state->dir);
+ pg_free(state);
+}

-- 
Regards,
Dilip Kumar
Google