From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
cc: kuzmin.db4@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #19438: segfault with temp_file_limit inside cursor
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References: <19438-9d37b179c56d43aa@postgresql.org> <1106026.1774573371@sss.pgh.pa.us> <1338824.1774633289@sss.pgh.pa.us> <CAApHDvox3Ro8mZJxignuyB-dGXJ9=wQNEkOFni9025GP=rOKkg@mail.gmail.com> <1830345.1774798374@sss.pgh.pa.us> <CAApHDvrdPriH6MO=YGEh9=KVDnDtqZyW4VuRXkmBS8WnRFessA@mail.gmail.com>
Comments: In-reply-to David Rowley <dgrowleyml@gmail.com>
	message dated "Mon, 30 Mar 2026 12:41:37 +1300"
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Date: Sun, 29 Mar 2026 19:51:12 -0400
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David Rowley <dgrowleyml@gmail.com> writes:
> I looked at the code and tested.  The only thing that I noted was
> GenerationFree(), where we do:

> /* Test for previously-freed chunk */
> if (unlikely(chunk->requested_size == InvalidAllocSize))
>     elog(WARNING, "detected double pfree in %s %p",
>          ((MemoryContext) block->context)->name, chunk);
> /* Test for someone scribbling on unused space in chunk */
> Assert(chunk->requested_size < chunksize);

> I expect you've likely thought of this, but if we do spit out the
> warning there, then the Assert is definitely going to fail, as
> InvalidAllocSize is defined as SIZE_MAX.

Yeah, I saw that after sending the patch.  Not only would that
Assert fail, but without it, code below would go nuts too.

> I don't know if that means
> it's worth deviating from the similar WARNINGs you've added and making
> that one an ERROR. There's certainly no guarantee with the other
> context that we'll not crash sometime very soon after issuing the
> warning anyway, so maybe it's fine.

Seems like a reasonable answer.  What do you think of making the
double-free cases ERRORs across the board?  If we don't error out,
there will likely be cascading problems in all the mcxt types not
just this one.

			regards, tom lane