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
In-reply-to: <1830345.1774798374@sss.pgh.pa.us>
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>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Sun, 29 Mar 2026 11:32:54 -0400"
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Date: Sun, 29 Mar 2026 12:25:38 -0400
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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 =3D palloc_aligned(...);
	pfree(p);
	pfree(p);

I got

ERROR:  pfree called with invalid pointer 0x1f286b0 (header 0x7f7f7f7f7f7f=
7f7f)

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