Horton

Re: BUG #16329: Valgrind detects an invalid read when building a gist index with buffering

Alexander Law <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: pgsql-bugs@lists.postgresql.org
Date: 2020-03-30T05:00:00Z
Lists: pgsql-bugs 
30.03.2020 00:00, PG Bug reporting form wrote:
> The following bug has been logged on the website:
>
> Bug reference:      16329
> Logged by:          Alexander Lakhin
> Email address:      exclusion@gmail.com
> PostgreSQL version: 12.2
> Operating system:   Ubuntu 18.04
> Description:        
>
> Running the following query under valgrind:
> create table gist_point_tbl(id int4, p point);
> insert into gist_point_tbl (id, p)
> select g, point(g*10+1, g*10+1) from generate_series(1, 30000) g;
> create index gist_pointidx2 on gist_point_tbl using gist(p) with (buffering
> = on, fillfactor=50);
>
> leads to a memory access error:
> ==00:00:00:08.755 18585== Invalid read of size 2
> ==00:00:00:08.756 18585==    at 0x1F94CA: gistBuildCallback
> (gistbuild.c:495)
I've found that the memory context where the itup is created:
    oldCtx = MemoryContextSwitchTo(buildstate->giststate->tempCxt);

    /* form an index tuple and point it at the heap tuple */
    itup = gistFormTuple(buildstate->giststate, index, values, isnull,
true);

can be reset in gistBufferingBuildInsert->gistProcessEmptyingQueue:
            /* Free all the memory allocated during index tuple
processing */
            MemoryContextReset(buildstate->giststate->tempCxt);

Probably, the offending commit is d22a09dc.

Commits

  1. Fix dereference of dangling pointer in GiST index buffering build.

  2. Fix GiST buffering build to work when there are included columns.

  3. Re-allow testing of GiST buffered builds.

  4. Add support for building GiST index by sorting.