OK, it looks like assertion is being caused by the legacy NVIDIA GL library:
(gdb) thread apply all bt
Thread 1 (process 5358):
#0 0xb7f30410 in __kernel_vsyscall ()
#1 0xb7d92df0 in raise () from /lib/tls/i686/cmov/libc.so.6
#2 0xb7d94641 in abort () from /lib/tls/i686/cmov/libc.so.6
#3 0xb7d8c43b in __assert_fail () from /lib/tls/i686/cmov/libc.so.6
#4 0xb74ef6f4 in xcb_xlib_lock () from /usr/lib/libxcb-xlib.so.0
#5 0xb7cc0c8c in _XCBLockDisplay (dpy=0x804cb30) at ../../src/xcb_lock.c:20
#6 0xb7ca4241 in XESetCloseDisplay (dpy=0x804c340, extension=1, proc=0)
at ../../src/InitExt.c:231
#7 0xb7edaa69 in ?? () from /usr/lib/libGL.so.1
#8 0x0804c340 in ?? ()
#9 0x00000001 in ?? ()
#10 0x00000000 in ?? ()
Using
LD_PRELOAD=/usr/lib/nvidia/libGL.so.1.2.xlibmesa glxgears
(thus using the original mesa GL library) makes the assertion part of this problem disappear.
OK, it looks like assertion is being caused by the legacy NVIDIA GL library:
(gdb) thread apply all bt
Thread 1 (process 5358): i686/cmov/ libc.so. 6 i686/cmov/ libc.so. 6 i686/cmov/ libc.so. 6 libxcb- xlib.so. 0 xcb_lock. c:20 InitExt. c:231
#0 0xb7f30410 in __kernel_vsyscall ()
#1 0xb7d92df0 in raise () from /lib/tls/
#2 0xb7d94641 in abort () from /lib/tls/
#3 0xb7d8c43b in __assert_fail () from /lib/tls/
#4 0xb74ef6f4 in xcb_xlib_lock () from /usr/lib/
#5 0xb7cc0c8c in _XCBLockDisplay (dpy=0x804cb30) at ../../src/
#6 0xb7ca4241 in XESetCloseDisplay (dpy=0x804c340, extension=1, proc=0)
at ../../src/
#7 0xb7edaa69 in ?? () from /usr/lib/libGL.so.1
#8 0x0804c340 in ?? ()
#9 0x00000001 in ?? ()
#10 0x00000000 in ?? ()
Using /usr/lib/ nvidia/ libGL.so. 1.2.xlibmesa glxgears
LD_PRELOAD=
(thus using the original mesa GL library) makes the assertion part of this problem disappear.