Re: bug in SlabAlloc / VALGRIND_MAKE_MEM_DEFINED

Andres Freund <andres@anarazel.de>

From: Andres Freund <andres@anarazel.de>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: PostgreSQL Developers <pgsql-hackers@postgresql.org>
Date: 2017-04-04T21:46:28Z
Lists: pgsql-hackers
On 2017-04-04 23:23:30 +0200, Tomas Vondra wrote:
> On 04/04/2017 10:42 PM, Tomas Vondra wrote:
> > Hi,
> > 
> > Andres nagged to me about valgrind runs taking much longer since
> > 9fab40ad introduced the SlabContext into reorderbuffer.c. And by
> > "longer" I mean hours instead of minutes.
> > 
> > After a bit of investigation I stumbled on this line in slab.c:
> > 
> >   VALGRIND_MAKE_MEM_DEFINED(chunk, SlabChunkGetPointer(chunk));
> > 
> > which is wrong, because the second parameter should be size and not
> > another pointer. This essentially marks a lot of memory as defined,
> > which results in the extreme test runtime.
> > 
> > Instead, the line should be:
> > 
> >   VALGRIND_MAKE_MEM_DEFINED(SlabChunkGetPointer(chunk), sizeof(int32));
> > 
> > Patch attached.
> > 
> 
> Turns out SlabCheck() was missing VALGRIND_MAKE_MEM_DEFINED, resulting in a
> valgrind failure with --enable-assert. Updated patch version attached,
> passing all tests in test_decoding.

Pushed, and re-enabled TestDecoding on skink.


Commits

  1. Fix two valgrind issues in slab allocator.