From: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
Subject: Re: pread() and pwrite()
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: jesper.pedersen@redhat.com, Thomas Munro <thomas.munro@enterprisedb.com>,
 Alvaro Herrera <alvherre@2ndquadrant.com>,
 Magnus Hagander <magnus@hagander.net>, Oskari Saarenmaa <os@ohmu.fi>,
 Pg Hackers <pgsql-hackers@postgresql.org>,
 Tobias Oberstein <tobias.oberstein@gmail.com>
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 <856530e2-260d-1d61-ec18-595778868a1b@redhat.com>
 <CAEepm=0+GizsKRRd=7wrL0n8VMKadR0=o99VWiXD58oJyJOUCQ@mail.gmail.com>
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 <26123.1541601037@sss.pgh.pa.us>
Message-ID: <6b69fc80-03c2-b445-907d-89cdbde7f1fa@2ndQuadrant.com>
Date: Wed, 7 Nov 2018 10:03:39 -0500
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On 11/7/18 9:30 AM, Tom Lane wrote:
> Andrew Dunstan <andrew.dunstan@2ndquadrant.com> writes:
>> On 11/7/18 7:26 AM, Jesper Pedersen wrote:
>>> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=skink&dt=2018-11-07%2001%3A01%3A01
>> And lousyjack, which uses a slightly different way of calling valgrind,
>> and thus got past initdb, found a bunch more:
>> <https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=lousyjack&dt=2018-11-07%2001%3A33%3A01>
> I'm confused by this.  Surely the pwrite-based code is writing exactly the
> same data as before.  Do we have to conclude that valgrind is complaining
> about passing uninitialized data to pwrite() when it did not complain
> about exactly the same thing for write()?
>
> [ looks ... ]  No, what we have to conclude is that the write-related
> suppressions in src/tools/valgrind.supp need to be replaced or augmented
> with pwrite-related ones.


Yeah. I just trawled through the lousyjack logs and it looks like all 
the cases it reported could be handled by:

{
     padding_XLogRecData_pwrite
     Memcheck:Param
     pwrite64(buf)

     ...
     fun:XLogWrite
}

cheers


andrew

-- 
Andrew Dunstan                https://www.2ndQuadrant.com
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