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

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