MIME-Version: 1.0
References: <18374-ebb8113ce4d02f0d@postgresql.org> <3120721.1709395887@sss.pgh.pa.us>
 <b1a1eaf3-d5b7-da52-6bb7-c5b3fbe47f3e@gmail.com> <3140126.1709405398@sss.pgh.pa.us>
 <3148162.1709409519@sss.pgh.pa.us> <3399097.1709501969@sss.pgh.pa.us>
In-Reply-To: <3399097.1709501969@sss.pgh.pa.us>
From: Alexander Korotkov <aekorotkov@gmail.com>
Date: Wed, 6 Mar 2024 22:24:03 +0200
Message-ID: <CAPpHfduPAmF95Zg=sMfhBW+0Q=Bq2KKzF7AamvTQ0UDm80ZOLA@mail.gmail.com>
Subject: Re: BUG #18374: Printing memory contexts on OOM condition might lead
 to segmentation fault
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alexander Lakhin <exclusion@gmail.com>, pgsql-bugs@lists.postgresql.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: <https://www.postgresql.org/message-id/CAPpHfduPAmF95Zg%3DsMfhBW%2B0Q%3DBq2KKzF7AamvTQ0UDm80ZOLA%40mail.gmail.com>
Precedence: bulk

On Sun, Mar 3, 2024 at 11:39=E2=80=AFPM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I do think it's probably worth reducing MemoryContextDelete's stack
> usage to O(1), just to ensure we can't get into stack trouble during
> transaction abort.  That's not hard at all, as attached.
>
> I tried to make MemoryContextResetChildren work similarly, but that
> doesn't work because if we're not removing child contexts then we
> need extra state to tell which ones we've done already.  For the
> same reason my idea for bounding the stack space needed by
> MemoryContextStats doesn't seem to work.  We could possibly make it
> work if we were willing to add a temporary-use pointer field to all
> MemoryContext headers, but I'm unconvinced that'd be a good tradeoff.

For removing recursion from memory context processing, please check
the patch by Heikki [1], and my slightly revised version [2].

Links.
1. https://www.postgresql.org/message-id/6b48c746-9704-46dc-b9be-01fe4137c8=
24%40iki.fi
2. https://www.postgresql.org/message-id/CAPpHfdtQVzkKgrxqKZE9yESnu7cAATVQb=
GktVOSXPNWG7GOkhA%40mail.gmail.com

------
Regards,
Alexander Korotkov