Re: BUG #19438: segfault with temp_file_limit inside cursor

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