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: 2026-03-29T16:25:38Z
Lists: pgsql-bugs 
I wrote:
> ... I don't think alignedalloc.c
> needs its own defense either: it can rely on the underlying
> context type.

I started to wonder if an explicit test in AlignedAllocFree
could be useful anyway to make such problems a bit less obscure.
However, when I tried

	p = palloc_aligned(...);
	pfree(p);
	pfree(p);

I got

ERROR:  pfree called with invalid pointer 0x1f286b0 (header 0x7f7f7f7f7f7f7f7f)

That is, we'll never get to AlignedAllocFree because the underlying
context would have wipe_mem'd the aligned chunk's header during the
first pfree.  The only case in which such a test could be helpful is
in a build with MEMORY_CONTEXT_CHECKING but not CLOBBER_FREED_MEMORY.
While I suppose some people might build that way, it's got to be such
a tiny minority as to not be worth worrying about.

			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