[BUGS] overwriting an existing .so while being used crashes the server process

[Tomas Vondra]

Hi,

whenever I run a C-function (part of an .so file) and the file is
overwritten, the connection crashes. Tested on 9.1.3 and 9.2-beta1.

It's 100% reproducible:

 1) compile the attached file and copy the .so to pkglibdir

    $ gcc -I/home/tomas/tmp/postgresql-9.1.2/src/include testcomp.c
          -shared -fPIC -o testcomp.so

    $ cp testcomp.so `pg_config --pkglibdir`

 2) create a function, calling the .so

    CREATE FUNCTION test_computation()
           RETURNS void
           AS 'testcomp','test_computation'
           LANGUAGE C STRICT;

 3) call the function and while it's running, repeat step (1).

 4) an example of the output

    WARNING:  i = 532000000 v = 141512000266000000
    WARNING:  i = 533000000 v = 142044500266500000
    WARNING:  i = 534000000 v = 142578000267000000
    The connection to the server was lost. Attempting reset: Failed.

    and a log says this

    LOG:  server process (PID 17161) was terminated by signal 7: Bus
          error
    LOG:  terminating any other active server processes
    WARNING:  terminating connection because of crash of another server
              process
    ...

This does not happen when the .so is removed or just touched, it needs
to be overwritten (although with a file that's binary exactly the same).

Basic info about the box: Linux rimmer 3.3.2-gentoo #1 SMP PREEMPT Wed
Apr 18 14:54:04 CEST 2012 x86_64 Intel(R) Core(TM) i5-2500K CPU @
3.30GHz GenuineIntel GNU/Linux

kind regards
Tomas

#include <stdio.h>
#include <stdlib.h>

#include "postgres.h"
#include "funcapi.h"
#include "miscadmin.h"

PG_MODULE_MAGIC;

/*
 * gcc -I/home/tomas/tmp/postgresql-9.1.2/src/include testcomp.c -shared -fPIC
 *     -o testcomp.so
 * 
 *     CREATE FUNCTION test_computation()
 *         RETURNS void
 *         AS 'testcomp','test_computation'
 *         LANGUAGE C STRICT;
 * 
 * 
 */

PG_FUNCTION_INFO_V1(test_computation);

Datum test_computation(PG_FUNCTION_ARGS);
void *print_message_function( void *ptr );

Datum test_computation(PG_FUNCTION_ARGS)
{	
	int64 result;
	
	char * message1 = print_message_function(&result);
	
	PG_RETURN_VOID();
}
 
void *print_message_function( void *ptr )
{
	int64 i;
	int64 x = 0;
	
	/* let's torture the CPU a bit ... */
	for (i = 0; i < 5000000000; i++) {
		
		x = x + i;
		
		if (i % 1000000 == 0) {
			/* needed for a quick response to cancel-query */
			elog(WARNING, "i = %ld v = %ld", i, x);
		}
		
		
	}
	
	*((int64*)ptr) = x;
	
}

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