Horton

Re: PostgreSQL crashes with SIGSEGV

Peter Geoghegan <pg@bowt.ie>

View thread View on postgr.es
From: Peter Geoghegan <pg@bowt.ie>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Aleksandr Parfenov <a.parfenov@postgrespro.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2018-02-06T22:27:47Z
Lists: pgsql-bugs, pgsql-hackers 
On Wed, Jan 17, 2018 at 2:23 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> A complicating factor for this fix of mine is that mode_final() seems
> to have its own ideas about tuple memory lifetime, over and above what
> tuplesort_getdatum() explicitly promises, as can be seen here:
>
> /*
>  * Note: we *cannot* clean up the tuplesort object here, because the value
>  * to be returned is allocated inside its sortcontext.  We could use
>  * datumCopy to copy it out of there, but it doesn't seem worth the
>  * trouble, since the cleanup callback will clear the tuplesort later.
>  */

> ISTM that either grouping sets or mode_final() must necessarily be
> wrong, because each oversteps, and infers a different contract from
> tuplesort tuple fetching routines (different assumptions about memory
> contexts are made in each case). Only one can be right, unless it's
> okay to have one rule for tuplesort_getdatum() and another for
> tuplesort_gettupleslot() (which seems questionable to me). I still
> think that grouping sets is right (and that mode_final() is wrong). Do
> you?

It would be nice to get an opinion on this mode_final() + tuplesort
memory lifetime business from you, Tom.

Note that you removed the quoted comment within be0ebb65, back in October.

-- 
Peter Geoghegan

Commits

  1. Fix actual and potential double-frees around tuplesort usage.

  2. Allow the built-in ordered-set aggregates to share transition state.

  3. Avoid integer overflow while sifting-up a heap in tuplesort.c.

  4. Allow avoiding tuple copy within tuplesort_gettupleslot().

  5. Remove should_free arguments to tuplesort routines.

  6. Fix use-after-free around DISTINCT transition function calls.

  7. Reuse abbreviated keys in ordered [set] aggregates.