My gnome-shell session hung after some package-update related dialog asked me for my password because of untrusted sources. It seems as if the dialog froze the system, because the screen doesn't update at all. All other processes on the system are fine, i.e. sshd. I tried to pm-suspend and it worked after a good while. But after resume, the screen went with lovely black and white stripes while the system otherwise worked normally. I tried to pm-hibernate but it then froze completely.

I attached gdb to the X server just before I suspended:

muelli@bigbox ~ $   sudo gdb -p `pgrep X`
[sudo] password for muelli: 
GNU gdb (GDB) Fedora (7.3.1-46.fc15)
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
22494: No such file or directory.
Attaching to process 1414
Reading symbols from /usr/bin/Xorg...Reading symbols from /usr/lib/debug/usr/bin/Xorg.debug...done.
done.
Reading symbols from /lib64/libudev.so.0...Reading symbols from /usr/lib/debug/lib64/libudev.so.0.11.1.debug...done.
done.
Loaded symbols for /lib64/libudev.so.0
Reading symbols from /lib64/libcrypto.so.10...Reading symbols from /usr/lib/debug/lib64/libcrypto.so.1.0.0e.debug...done.
done.
Loaded symbols for /lib64/libcrypto.so.10
Reading symbols from /lib64/libdl.so.2...Reading symbols from /usr/lib/debug/lib64/libdl-2.14.so.debug...done.
done.
Loaded symbols for /lib64/libdl.so.2
Reading symbols from /usr/lib64/libpciaccess.so.0...Reading symbols from /usr/lib/debug/usr/lib64/libpciaccess.so.0.10.8.debug...done.
done.
Loaded symbols for /usr/lib64/libpciaccess.so.0
Reading symbols from /lib64/libpthread.so.0...Reading symbols from /usr/lib/debug/lib64/libpthread-2.14.so.debug...done.
[Thread debugging using libthread_db enabled]
done.
Loaded symbols for /lib64/libpthread.so.0
Reading symbols from /usr/lib64/libpixman-1.so.0...Reading symbols from /usr/lib/debug/usr/lib64/libpixman-1.so.0.20.2.debug...done.
done.
Loaded symbols for /usr/lib64/libpixman-1.so.0
Reading symbols from /usr/lib64/libXfont.so.1...Reading symbols from /usr/lib/debug/usr/lib64/libXfont.so.1.4.1.debug...done.
done.
Loaded symbols for /usr/lib64/libXfont.so.1
Reading symbols from /usr/lib64/libXau.so.6...Reading symbols from /usr/lib/debug/usr/lib64/libXau.so.6.0.0.debug...done.
done.
Loaded symbols for /usr/lib64/libXau.so.6
Reading symbols from /usr/lib64/libXdmcp.so.6...Reading symbols from /usr/lib/debug/usr/lib64/libXdmcp.so.6.0.0.debug...done.
done.
Loaded symbols for /usr/lib64/libXdmcp.so.6
Reading symbols from /lib64/libaudit.so.1...Reading symbols from /usr/lib/debug/lib64/libaudit.so.1.0.0.debug...done.
done.
Loaded symbols for /lib64/libaudit.so.1
Reading symbols from /lib64/libm.so.6...Reading symbols from /usr/lib/debug/lib64/libm-2.14.so.debug...done.
done.
Loaded symbols for /lib64/libm.so.6
Reading symbols from /lib64/librt.so.1...Reading symbols from /usr/lib/debug/lib64/librt-2.14.so.debug...done.
done.
Loaded symbols for /lib64/librt.so.1
Reading symbols from /lib64/libc.so.6...Reading symbols from /usr/lib/debug/lib64/libc-2.14.so.debug...done.
done.
Loaded symbols for /lib64/libc.so.6
Reading symbols from /lib64/libgcc_s.so.1...Reading symbols from /usr/lib/debug/lib64/libgcc_s-4.6.1-20110908.so.1.debug...done.
done.
Loaded symbols for /lib64/libgcc_s.so.1
Reading symbols from /lib64/libz.so.1...Reading symbols from /usr/lib/debug/lib64/libz.so.1.2.5.debug...done.
done.
Loaded symbols for /lib64/libz.so.1
Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug/lib64/ld-2.14.so.debug...done.
done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Reading symbols from /usr/lib64/libfreetype.so.6...Reading symbols from /usr/lib/debug/usr/lib64/libfreetype.so.6.6.2.debug...done.
done.
Loaded symbols for /usr/lib64/libfreetype.so.6
Reading symbols from /usr/lib64/libfontenc.so.1...Reading symbols from /usr/lib/debug/usr/lib64/libfontenc.so.1.0.0.debug...done.
done.
Loaded symbols for /usr/lib64/libfontenc.so.1
Reading symbols from /usr/lib64/xorg/modules/extensions/libextmod.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/extensions/libextmod.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/extensions/libextmod.so
Reading symbols from /lib64/libselinux.so.1...Reading symbols from /usr/lib/debug/lib64/libselinux.so.1.debug...done.
done.
Loaded symbols for /lib64/libselinux.so.1
Reading symbols from /usr/lib64/xorg/modules/extensions/libdbe.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/extensions/libdbe.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/extensions/libdbe.so
Reading symbols from /usr/lib64/xorg/modules/extensions/libglx.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/extensions/libglx.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/extensions/libglx.so
Reading symbols from /usr/lib64/xorg/modules/extensions/librecord.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/extensions/librecord.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/extensions/librecord.so
Reading symbols from /usr/lib64/xorg/modules/extensions/libdri.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/extensions/libdri.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/extensions/libdri.so
Reading symbols from /usr/lib64/libdrm.so.2...Reading symbols from /usr/lib/debug/usr/lib64/libdrm.so.2.4.0.debug...done.
done.
Loaded symbols for /usr/lib64/libdrm.so.2
Reading symbols from /usr/lib64/xorg/modules/extensions/libdri2.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/extensions/libdri2.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/extensions/libdri2.so
Reading symbols from /usr/lib64/xorg/modules/drivers/nouveau_drv.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/drivers/nouveau_drv.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/drivers/nouveau_drv.so
Reading symbols from /usr/lib64/libdrm_nouveau.so.1...Reading symbols from /usr/lib/debug/usr/lib64/libdrm_nouveau.so.1.0.0.debug...done.
done.
Loaded symbols for /usr/lib64/libdrm_nouveau.so.1
Reading symbols from /usr/lib64/xorg/modules/drivers/vesa_drv.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/drivers/vesa_drv.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/drivers/vesa_drv.so
Reading symbols from /usr/lib64/xorg/modules/drivers/fbdev_drv.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/drivers/fbdev_drv.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/drivers/fbdev_drv.so
Reading symbols from /usr/lib64/xorg/modules/libfbdevhw.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/libfbdevhw.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/libfbdevhw.so
Reading symbols from /usr/lib64/xorg/modules/libfb.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/libfb.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/libfb.so
Reading symbols from /usr/lib64/xorg/modules/libexa.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/libexa.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/libexa.so
Reading symbols from /usr/lib64/xorg/modules/libshadowfb.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/libshadowfb.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/libshadowfb.so
Reading symbols from /usr/lib64/dri/nouveau_dri.so...Reading symbols from /usr/lib/debug/usr/lib64/dri/nouveau_dri.so.debug...done.
done.
Loaded symbols for /usr/lib64/dri/nouveau_dri.so
Reading symbols from /lib64/libexpat.so.1...Reading symbols from /usr/lib/debug/lib64/libexpat.so.1.5.2.debug...done.
done.
Loaded symbols for /lib64/libexpat.so.1
Reading symbols from /usr/lib64/llvm/libLLVM-2.8.so...Reading symbols from /usr/lib/debug/usr/lib64/llvm/libLLVM-2.8.so.debug...done.
done.
Loaded symbols for /usr/lib64/llvm/libLLVM-2.8.so
Reading symbols from /usr/lib64/libstdc++.so.6...Reading symbols from /usr/lib/debug/usr/lib64/libstdc++.so.6.0.16.debug...done.
done.
Loaded symbols for /usr/lib64/libstdc++.so.6
Reading symbols from /usr/lib64/libffi.so.5...Reading symbols from /usr/lib/debug/usr/lib64/libffi.so.5.0.10.debug...done.
done.
Loaded symbols for /usr/lib64/libffi.so.5
Reading symbols from /usr/lib64/xorg/modules/input/evdev_drv.so...Reading symbols from /usr/lib/debug/usr/lib64/xorg/modules/input/evdev_drv.so.debug...done.
done.
Loaded symbols for /usr/lib64/xorg/modules/input/evdev_drv.so
Reading symbols from /lib64/libnss_files.so.2...Reading symbols from /usr/lib/debug/lib64/libnss_files-2.14.so.debug...done.
done.
Loaded symbols for /lib64/libnss_files.so.2
0x0000003b41ad8af7 in ioctl () at ../sysdeps/unix/syscall-template.S:82
82      T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
warning: not using untrusted file ".gdbinit"
(gdb) bt
#0  0x0000003b41ad8af7 in ioctl () at ../sysdeps/unix/syscall-template.S:82
#1  0x0000003030003358 in drmIoctl (fd=8, request=1074291842, 
    arg=0x7fff2e856c20) at xf86drm.c:167
#2  0x000000303000547b in drmCommandWrite (fd=<optimized out>, 
    drmCommandIndex=<optimized out>, data=<optimized out>, 
    size=<optimized out>) at xf86drm.c:2378
#3  0x00007fce613eaed7 in nouveau_bo_wait (bo=0x1ac36f0, cpu_write=0, 
    no_wait=<optimized out>, no_block=<optimized out>) at nouveau_bo.c:390
#4  0x00007fce613eb4f9 in nouveau_bo_map_range (bo=0x1ac36f0, delta=0, 
    size=<optimized out>, flags=4) at nouveau_bo.c:433
#5  0x00007fce61626ddb in NVAccelDownloadM2MF (dst_pitch=248, 
    dst=0x1e73a20 "", h=1, w=62, y=0, x=0, pspix=0x3a65260)
    at nouveau_exa.c:132
#6  nouveau_exa_download_from_screen (pspix=0x3a65260, x=0, y=0, w=62, h=1, 
    dst=0x1e73a20 "", dst_pitch=248) at nouveau_exa.c:386
#7  0x00007fce609aaf60 in exaGetImage (pDrawable=0x3a65260, x=0, y=0, w=62, 
    h=1, format=2, planeMask=4294967295, d=0x1e73a20 "") at exa_accel.c:1296
#8  0x00000000005565b5 in miSpriteGetImage (pDrawable=0x3a65260, sx=0, sy=0, 
    w=62, h=1, format=2, planemask=4294967295, pdstLine=0x1e73a20 "")
    at misprite.c:433
#9  0x00000000004a4555 in compGetImage (pDrawable=0x3a65260, 
---Type <return> to continue, or q <return> to quit---
    sx=<optimized out>, sy=<optimized out>, w=<optimized out>, 
    h=<optimized out>, format=<optimized out>, planemask=4294967295, 
    pdstLine=0x1e73a20 "") at compinit.c:149
#10 0x000000000042c0c3 in DoGetImage (planemask=<optimized out>, 
    height=<optimized out>, width=<optimized out>, y=0, x=0, 
    drawable=<optimized out>, format=<optimized out>, client=0x2d3d050, 
    im_return=<optimized out>) at dispatch.c:2156
#11 ProcGetImage (client=0x2d3d050) at dispatch.c:2243
#12 0x000000000042edb1 in Dispatch () at dispatch.c:431
#13 0x0000000000422e1a in main (argc=<optimized out>, argv=0x7fff2e857138, 
    envp=<optimized out>) at main.c:287
(gdb) t a a bt full

Thread 1 (Thread 0x7fce625088a0 (LWP 1414)):
#0  0x0000003b41ad8af7 in ioctl () at ../sysdeps/unix/syscall-template.S:82
No locals.
#1  0x0000003030003358 in drmIoctl (fd=8, request=1074291842, 
    arg=0x7fff2e856c20) at xf86drm.c:167
        ret = <optimized out>
#2  0x000000303000547b in drmCommandWrite (fd=<optimized out>, 
    drmCommandIndex=<optimized out>, data=<optimized out>, 
    size=<optimized out>) at xf86drm.c:2378
        request = <optimized out>
#3  0x00007fce613eaed7 in nouveau_bo_wait (bo=0x1ac36f0, cpu_write=0, 
    no_wait=<optimized out>, no_block=<optimized out>) at nouveau_bo.c:390
        nvdev = 0x1ab48f0
        nvbo = 0x1ac36f0
        req = {handle = 9, flags = 0}
        ret = <optimized out>
#4  0x00007fce613eb4f9 in nouveau_bo_map_range (bo=0x1ac36f0, delta=0, 
    size=<optimized out>, flags=4) at nouveau_bo.c:433
        nvbo = 0x1ac36f0
        ret = <optimized out>
---Type <return> to continue, or q <return> to quit---
#5  0x00007fce61626ddb in NVAccelDownloadM2MF (dst_pitch=248, 
    dst=0x1e73a20 "", h=1, w=62, y=0, x=0, pspix=0x3a65260)
    at nouveau_exa.c:132
        i = <optimized out>
        src = <optimized out>
        m2mf = 0x1abe460
        cpp = 4
        src_offset = 0
        line_count = <optimized out>
        pScrn = <optimized out>
        chan = 0x1abecb0
        linear = 1
        pNv = 0x1ab43f0
        bo = 0x24aeaf0
        line_len = 248
        src_pitch = 256
#6  nouveau_exa_download_from_screen (pspix=0x3a65260, x=0, y=0, w=62, h=1, 
    dst=0x1e73a20 "", dst_pitch=248) at nouveau_exa.c:386
        pNv = <optimized out>
        bo = 0x1abecb0
        src_pitch = 256
---Type <return> to continue, or q <return> to quit---
        cpp = 4
        offset = 0
        src = <optimized out>
        ret = 780495904
#7  0x00007fce609aaf60 in exaGetImage (pDrawable=0x3a65260, x=0, y=0, w=62, 
    h=1, format=2, planeMask=4294967295, d=0x1e73a20 "") at exa_accel.c:1296
        pExaScr = 0xffffffffffffffff
        pPix = <optimized out>
        pExaPixmap = 0x7fff2e856c20
        xoff = 0
        yoff = 0
        ok = <optimized out>
#8  0x00000000005565b5 in miSpriteGetImage (pDrawable=0x3a65260, sx=0, sy=0, 
    w=62, h=1, format=2, planemask=4294967295, pdstLine=0x1e73a20 "")
    at misprite.c:433
        pScreen = 0x1abe9b0
        pDev = <optimized out>
        pCursorInfo = <optimized out>
        pPriv = 0x1ad6180
#9  0x00000000004a4555 in compGetImage (pDrawable=0x3a65260, 
    sx=<optimized out>, sy=<optimized out>, w=<optimized out>, 
---Type <return> to continue, or q <return> to quit---
    h=<optimized out>, format=<optimized out>, planemask=4294967295, 
    pdstLine=0x1e73a20 "") at compinit.c:149
        pScreen = 0x1abe9b0
        cs = 0x1af8900
#10 0x000000000042c0c3 in DoGetImage (planemask=<optimized out>, 
    height=<optimized out>, width=<optimized out>, y=0, x=0, 
    drawable=<optimized out>, format=<optimized out>, client=0x2d3d050, 
    im_return=<optimized out>) at dispatch.c:2156
        linesPerBuf = 1
        linesDone = 0
        rely = <optimized out>
        nlines = 1
        rc = 0
        widthBytesLine = 248
        xgi = {type = 1 '\001', depth = 32 ' ', sequenceNumber = 54622, 
          length = 62, visual = 0, pad3 = 0, pad4 = 0, pad5 = 0, pad6 = 0, 
          pad7 = 0}
        length = <optimized out>
        pVisibleRegion = 0x0
        pDraw = 0x3a65260
        pBoundingDraw = <optimized out>
---Type <return> to continue, or q <return> to quit---
        relx = <optimized out>
        plane = 0
        pBuf = 0x1e73a20 ""
#11 ProcGetImage (client=0x2d3d050) at dispatch.c:2243
        stuff = <optimized out>
#12 0x000000000042edb1 in Dispatch () at dispatch.c:431
        clientReady = 0x1d236f0
        result = <optimized out>
        client = 0x2d3d050
        nready = 0
        icheck = 0x7e4d30
        start_tick = 753600
#13 0x0000000000422e1a in main (argc=<optimized out>, argv=0x7fff2e857138, 
    envp=<optimized out>) at main.c:287
        i = <optimized out>
        alwaysCheckForInput = {0, 1}
(gdb) 
(gdb) n
84      T_PSEUDO_END (SYSCALL_SYMBOL)
(gdb) 
ioctl () at ../sysdeps/unix/syscall-template.S:83
83              ret
(gdb) 
drmIoctl (fd=8, request=1074291842, arg=0x7fff2e856c20) at xf86drm.c:168
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 
168         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
(gdb) 
167             ret = ioctl(fd, request, arg);
(gdb) 


Note that I have graphic problems anyway as described in bug 749986.