Comment 4 for bug 388357

Here is a backtrace of the X server at the time of the hang:

#0 0x00007feedbda0ec7 in ioctl () from /lib/libc.so.6
#1 0x00007feeda9812e3 in drmIoctl () from /usr/lib/libdrm.so.2
#2 0x00007feeda9815e6 in drmCommandNone () from /usr/lib/libdrm.so.2
#3 0x00007feeda50b370 in I830BlockHandler (i=0,
    blockData=<value optimized out>, pTimeout=0x7fff7b671df8,
    pReadmask=0x7dff80) at ../../src/i830_driver.c:2281
#4 0x0000000000536885 in AnimCurScreenBlockHandler (
    screenNum=<value optimized out>, blockData=<value optimized out>,
    pTimeout=<value optimized out>, pReadmask=<value optimized out>)
    at ../../render/animcur.c:222
#5 0x0000000000500d86 in compBlockHandler (i=0, blockData=0x0,
    pTimeout=0x7fff7b671df8, pReadmask=<value optimized out>)
    at ../../composite/compinit.c:158
#6 0x00000000004520e0 in BlockHandler (pTimeout=0x7fff7b671df8,
    pReadmask=0x7dff80) at ../../dix/dixutils.c:384
#7 0x00000000004eed31 in WaitForSomething (
    pClientsReady=<value optimized out>) at ../../os/WaitFor.c:215
#8 0x000000000044dd52 in Dispatch () at ../../dix/dispatch.c:367
#9 0x0000000000433f15 in main (argc=<value optimized out>,
    argv=0x7fff7b672018, envp=<value optimized out>) at ../../dix/main.c:397