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

On Wed, 4 Feb 2026 17:20:49 +0800
Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com> 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.

As far as I know, AllocSlruSegState() and FreeSlruWrite() are not called
repeatedly in a loop, and the amount of memory involved is small, so the
impact of the leak seems limited. That said, I agree that it is better to
also free the memory owned by the struct members.

Regards,
Yugo Nagata

>
> 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/
>
>
>
>

--
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>