Application: kwin (4.6.3 (4.6.3))
KDE Platform Version: 4.6.3 (4.6.3)
Qt Version: 4.7.3
Operating System: Linux 2.6.38-2-686 i686
Distribution: Debian GNU/Linux unstable (sid)

-- Information about the crash:
- What I was doing when the application crashed:

Every time i turn on the Desktop Effects, KWin crashes. 
I have Direct Rendering working without problems

The crash can be reproduced every time.

-- Backtrace:
Application: KWin (kwin), signal: Segmentation fault
[Current thread is 1 (Thread 0xb233e940 (LWP 29916))]

Thread 2 (Thread 0xaef80b70 (LWP 29930)):
#0  0xb78b2424 in __kernel_vsyscall ()
#1  0xb363f20a in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/i686/cmov/libpthread.so.0
#2  0xb76cf9dd in pthread_cond_wait () from /lib/i686/cmov/libc.so.6
#3  0xb6d74b09 in ?? () from /usr/lib/libQtScript.so.4
#4  0xb6d74b4f in ?? () from /usr/lib/libQtScript.so.4
#5  0xb363ac39 in start_thread () from /lib/i686/cmov/libpthread.so.0
#6  0xb76c28ee in clone () from /lib/i686/cmov/libc.so.6

Thread 1 (Thread 0xb233e940 (LWP 29916)):
[KCrash Handler]
#7  radeonDRI2Flush (drawable=0x8581b88) at radeon_screen.c:394
#8  0xb69f04c1 in dri2SwapBuffers (pdraw=0x857f478, target_msc=0, divisor=0, remainder=0) at dri2_glx.c:539
#9  0xb69c9999 in glXSwapBuffers (dpy=0x8155160, drawable=69206050) at glxcmds.c:734
#10 0xb784ebbb in ?? () from /usr/lib/kde4/libkdeinit/libkdeinit4_kwin.so
#11 0xb784f446 in ?? () from /usr/lib/kde4/libkdeinit/libkdeinit4_kwin.so
#12 0xb7835064 in ?? () from /usr/lib/kde4/libkdeinit/libkdeinit4_kwin.so
#13 0xb651f084 in QObject::event(QEvent*) () from /usr/lib/libQtCore.so.4
#14 0xb5a34044 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#15 0xb5a393d2 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#16 0xb73b6de1 in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#17 0xb77c021f in ?? () from /usr/lib/kde4/libkdeinit/libkdeinit4_kwin.so
#18 0xb6506f7e in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#19 0xb6537440 in ?? () from /usr/lib/libQtCore.so.4
#20 0xb6537cdd in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#21 0xb5aea1ea in ?? () from /usr/lib/libQtGui.so.4
#22 0xb6505f9d in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#23 0xb65061e1 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#24 0xb650a94a in QCoreApplication::exec() () from /usr/lib/libQtCore.so.4
#25 0xb5a31ea4 in QApplication::exec() () from /usr/lib/libQtGui.so.4
#26 0xb77c2f17 in kdemain () from /usr/lib/kde4/libkdeinit/libkdeinit4_kwin.so
#27 0x0804856b in ?? ()
#28 0xb760ce46 in __libc_start_main () from /lib/i686/cmov/libc.so.6
#29 0x08048591 in _start ()

Reported using DrKonqi