Horton

Re: BUG #19438: segfault with temp_file_limit inside cursor

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
Cc: kuzmin.db4@gmail.com, pgsql-bugs@lists.postgresql.org
Date: 2026-03-29T23:51:12Z
Lists: pgsql-bugs 
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

Commits

  1. Be more careful to preserve consistency of a tuplestore.

  2. Detect pfree or repalloc of a previously-freed memory chunk.

  3. Improve performance of and reduce overheads of memory management