Description of problem:
Sorry,I'm not very sure how it happens,it simply reported to me after i had just run several normal programs such as web browsers and a pdf reader... 

Version-Release number of selected component:
xorg-x11-server-Xorg-1.12.3-2.fc17

Additional info:
libreport version: 2.0.13
abrt_version:   2.0.12
kernel:         3.5.4-1.fc17.i686.PAE

backtrace:
:0: /usr/bin/Xorg (xorg_backtrace+0x4a) [0x80ac45a]
:1: /usr/bin/Xorg (mieqEnqueue+0x22b) [0x81aacfb]
:2: /usr/bin/Xorg (0x8047000+0x4589c) [0x808c89c]
:3: /usr/bin/Xorg (xf86PostMotionEventM+0x253) [0x80d9ec3]
:4: /usr/lib/xorg/modules/input/evdev_drv.so (0xb6df5000+0x3e2e) [0xb6df8e2e]
:5: /usr/lib/xorg/modules/input/evdev_drv.so (0xb6df5000+0x5534) [0xb6dfa534]
:6: /usr/bin/Xorg (0x8047000+0x82302) [0x80c9302]
:7: /usr/bin/Xorg (0x8047000+0xa8693) [0x80ef693]
:8: (vdso) (__kernel_sigreturn+0x0) [0xb7724400]
:9: (vdso) (__kernel_vsyscall+0x10) [0xb7724424]
:10: /lib/libc.so.6 (ioctl+0x19) [0x4fa70459]
:11: /lib/libdrm.so.2 (drmIoctl+0x34) [0x42a21b74]
:12: /lib/libdrm.so.2 (drmCommandWriteRead+0x3d) [0x42a2469d]
:13: /lib/libdrm_radeon.so.1 (0xb74ce000+0x17c2) [0xb74cf7c2]
:14: /lib/libdrm_radeon.so.1 (radeon_bo_wait+0x1b) [0xb74d108b]
:15: /usr/lib/xorg/modules/drivers/radeon_drv.so (0xb74f3000+0xcb0d1) [0xb75be0d1]
:16: /usr/lib/xorg/modules/drivers/radeon_drv.so (0xb74f3000+0xcc042) [0xb75bf042]
:17: /usr/lib/xorg/modules/drivers/radeon_drv.so (0xb74f3000+0xd0164) [0xb75c3164]
:18: /lib/libdrm.so.2 (drmHandleEvent+0xd0) [0x42a26ee0]
:19: /usr/lib/xorg/modules/drivers/radeon_drv.so (0xb74f3000+0xcf6af) [0xb75c26af]
:20: /usr/bin/Xorg (WakeupHandler+0x6e) [0x807b64e]
:21: /usr/bin/Xorg (WaitForSomething+0x19b) [0x80a974b]
:22: /usr/bin/Xorg (0x8047000+0x30101) [0x8077101]
:23: /usr/bin/Xorg (0x8047000+0x1dce5) [0x8064ce5]
:24: /lib/libc.so.6 (__libc_start_main+0xf5) [0x4f99d635]
:25: /usr/bin/Xorg (0x8047000+0x1e029) [0x8065029]