Re: 回复: Fix segfault while accessing half-initialized hash table in pgstat_shmem.c

Hi Steven,

I think when an error is thrown within the PG_TRY block, the assignment to
shheader is interrupted and never completes. As a result, shheader retains
its initial, NULL value.

And, the PG_RE_THROW() within the PG_CATCH block causes a non-local jump,
immediately aborting the current execution path to handle the error at a
higher level. This guarantees that the code following PG_END_TRY is
unreachable in the error scenario.

Steven Niu <niushiji@gmail.com> 于2025年9月4日周四 15:38写道：

> _______________________________________
> From: Michael Paquier
> Sent: Thursday, September 04, 2025 14:30
> To: Steven Niu
> Cc: Mikhail Kot; pgsql-hackers@lists.postgresql.org; to@myrrc.dev
> Subject: Re: 回复: Fix segfault while accessing half-initialized hash table
> in pgstat_shmem.c
>
> On Thu, Sep 04, 2025 at 02:31:34AM +0000, Steven Niu wrote:
> > If pgstat_init_entry() errors on OOM, what would it returns to shheader,
> NULL?
> > That would bring trouble to dshash_delete_entry().
>
> Based on the proposal of patch 0002, the code would throw an error
> after cleaning up the shared memory state.  The generation and
> refcount number assigned inside pgstat_init_entry() would not matter
> as well because the entry created by dshash_find_or_insert() would be
> entirely gone.  So I am not sure what's the point you are trying to
> make here.
> --
> Michael
>
>
> Sorry, I made a mistake. I should say:
> "If pgstat_init_entry() errors on OOM, the local variable shheader may be
> NULL. This would bring trouble to pgstat_acquire_entry_ref() in the line 30
> of patch 002".
>