Message-ID: <475EA754.1090307@emolecules.com>
Date: Tue, 11 Dec 2007 07:05:56 -0800
From: Craig James <craig_james@emolecules.com>
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To: Alvaro Herrera <alvherre@alvh.no-ip.org>, pgsql-performance@postgresql.org
Subject: Re: libgcc double-free, backend won't die
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Alvaro Herrera wrote:
> Craig James wrote:
>> This is driving me crazy.  I have some Postgres C function extensions
>> in a shared library.  They've been working fine.  I upgraded to Fedora
>> Core 6 and gcc4, and now every time psql(1) disconnects from the
>> server, the serverlog gets this message:
>>
>>   *** glibc detected *** postgres: mydb mydb [local] idle: double free or corruption! (!prev): 0x08bfcde8
> 
> Do you have any Perl or Python functions or stuff like that?

There is one Perl function, but it is never invoked during this test.  I connect to Postgres, issue one "select myfunc()", and disconnect.

>>  Postgres 8.1.4
> 
> Please upgrade to 8.1.10 and try again.  If it still fails we will be
> much more interested in tracking it down.

Good idea, but alas, no difference.  I get the same "double free or corruption!" mesage.  I compiled 8.1.10 from source and installed, then rebuilt all of my code from scratch and reinstalled the shared object. Same message as before.

Here is my guess -- and this is just a guess.  My functions use a third-party library which, of necessity, uses malloc/free in the ordinary way.  I suspect that there's a bug in the Postgres palloc() code that's walking over memory that regular malloc() allocates.  The third-party library (OpenBabel) has been tested pretty thoroughly by me an others and has no memory corruption problems.  All malloc's are freed properly.  Does that seem like a possibility?

I can't figure out how to use ordinary tools like valgrind with a Postgres backend process to track this down.

Thanks,
Craig