I got some backtraces. They are slightly different depending on whether glxgears is run first or compiz. I reported the problem to linux-bugs(at)nvidia.com and hope they will come back to us:
$ glxgears
$ compiz
(gdb) symbol-file /usr/lib/debug/usr/bin/Xorg
(gdb) where
#0 0xb7db97cc in free () from /lib/tls/i686/cmov/libc.so.6
#1 0x081c3281 in Xfree (ptr=0xfffffffb) at ../../os/utils.c:1471
#2 0xb7216b06 in _nv002179X ()
from /usr/lib/xorg/modules/drivers//nvidia_drv.so
#3 0x00000003 in ?? ()
#4 0xb7217744 in ?? () from /usr/lib/xorg/modules/drivers//nvidia_drv.so
#5 0xbf921e88 in ?? ()
#6 0x00000000 in ?? ()
$ compiz
$ gtk-window-decorator
$ glxgears
(gdb) where
#0 0xb726e98a in _nv001744X ()
from /usr/lib/xorg/modules/drivers//nvidia_drv.so
#1 0xb726da34 in ?? () from /usr/lib/xorg/modules/drivers//nvidia_drv.so
#2 0x764b1210 in ?? ()
#3 0xb6370010 in ?? ()
#4 0x08215950 in ?? ()
#5 0x084fba78 in ?? ()
#6 0x084f05e8 in ?? ()
#7 0xb6370010 in ?? ()
#8 0x08215950 in ?? ()
#9 0x08205538 in ?? ()
#10 0x00000000 in ?? ()
I got some backtraces. They are slightly different depending on whether glxgears is run first or compiz. I reported the problem to linux-bugs( at)nvidia. com and hope they will come back to us:
$ glxgears debug/usr/ bin/Xorg i686/cmov/ libc.so. 6 utils.c: 1471 xorg/modules/ drivers/ /nvidia_ drv.so xorg/modules/ drivers/ /nvidia_ drv.so
$ compiz
(gdb) symbol-file /usr/lib/
(gdb) where
#0 0xb7db97cc in free () from /lib/tls/
#1 0x081c3281 in Xfree (ptr=0xfffffffb) at ../../os/
#2 0xb7216b06 in _nv002179X ()
from /usr/lib/
#3 0x00000003 in ?? ()
#4 0xb7217744 in ?? () from /usr/lib/
#5 0xbf921e88 in ?? ()
#6 0x00000000 in ?? ()
$ compiz decorator xorg/modules/ drivers/ /nvidia_ drv.so xorg/modules/ drivers/ /nvidia_ drv.so
$ gtk-window-
$ glxgears
(gdb) where
#0 0xb726e98a in _nv001744X ()
from /usr/lib/
#1 0xb726da34 in ?? () from /usr/lib/
#2 0x764b1210 in ?? ()
#3 0xb6370010 in ?? ()
#4 0x08215950 in ?? ()
#5 0x084fba78 in ?? ()
#6 0x084f05e8 in ?? ()
#7 0xb6370010 in ?? ()
#8 0x08215950 in ?? ()
#9 0x08205538 in ?? ()
#10 0x00000000 in ?? ()