More complete backtrace:

[Switching to Thread 0x7f1e743bc6f0 (LWP 6585)]
drm_intel_gem_bo_unreference_locked (bo=0x15d6e30) at intel_bufmgr_gem.c:585
585	intel_bufmgr_gem.c: No such file or directory.
	in intel_bufmgr_gem.c
(gdb) bt
#0  drm_intel_gem_bo_unreference_locked (bo=0x15d6e30) at intel_bufmgr_gem.c:585
#1  0x00007f1e7072b017 in drm_intel_gem_bo_unreference_locked (bo=0x1573b90) at intel_bufmgr_gem.c:561
#2  0x00007f1e7072b4ac in drm_intel_gem_bo_unreference (bo=0x1573b90) at intel_bufmgr_gem.c:599
#3  0x00007f1e7094ebc2 in intel_batch_flush (pScrn=0x1279760, flushed=<value optimized out>) at i830_batchbuffer.c:204
#4  0x00007f1e70959a1e in I830BlockHandler (i=0, blockData=0x0, pTimeout=0x7fff7c3edde8, pReadmask=0x7cb9c0) at i830_driver.c:2656
#5  0x00000000005134f9 in AnimCurScreenBlockHandler (screenNum=0, blockData=0x0, pTimeout=0x7fff7c3edde8, pReadmask=0x7cb9c0) at animcur.c:199
#6  0x00000000004ef931 in compBlockHandler (i=0, blockData=0x0, pTimeout=0x7fff7c3edde8, pReadmask=0x7cb9c0) at compinit.c:163
#7  0x000000000044c08f in BlockHandler (pTimeout=0x7fff7c3edde8, pReadmask=0x7cb9c0) at dixutils.c:383
#8  0x00000000004de78b in WaitForSomething (pClientsReady=0x1574050) at WaitFor.c:223
#9  0x00000000004487fb in Dispatch () at dispatch.c:375
#10 0x0000000000430735 in main (argc=9, argv=0x7fff7c3edfa8, envp=<value optimized out>) at main.c:438
(gdb) frame 0
#0  drm_intel_gem_bo_unreference_locked (bo=0x15d6e30) at intel_bufmgr_gem.c:585
585	in intel_bufmgr_gem.c
(gdb) info locals
bucket = (struct drm_intel_gem_bo_bucket *) 0x12836d0
tiling_mode = 0
bufmgr_gem = <value optimized out>
(gdb) p *$
The history is empty.
(gdb) p *$bucket
Attempt to take contents of a non-pointer value.
(gdb) p *bucket
$1 = {head = {prev = 0x7f1e7094ef90, next = 0x1279760}, max_entries = -1, num_entries = 1}
(gdb) x/5i $pc
0x7f1e7072b118 <drm_intel_gem_bo_unreference_locked+328>:	mov    %rdx,0x8(%rax)
0x7f1e7072b11c <drm_intel_gem_bo_unreference_locked+332>:	mov    %rdx,(%rbx)
0x7f1e7072b11f <drm_intel_gem_bo_unreference_locked+335>:	add    $0x18,%rsp
0x7f1e7072b123 <drm_intel_gem_bo_unreference_locked+339>:	pop    %rbx
0x7f1e7072b124 <drm_intel_gem_bo_unreference_locked+340>:	pop    %rbp
(gdb) p/x $rdx
$2 = 0x15d6eb0
(gdb) p/x $rax
$3 = 0x7f1e7094ef90
(gdb) source /tmp/
.ICE-unix/      .X0-lock        .X11-unix/      keyring-Fddiyp/ orbit-alex/     ssh-FczORk6606/ 
(gdb) directory ~alex/src/xorg
xorg/  xorg2/ 
(gdb) directory ~alex/src/xorg/
app/                               font/                              more_debug.log                     working.log
build.log                          git_xorg.sh                        old/                               working_vs_nonworking.txt
buildenv.sh                        hang_and_glitch.log                piglit/                            working_vs_nonworking_unified.txt
buildit.sh                         hw.txt                             pixman/                            xcb/
core                               install/                           proto/                             xkeyboard-config/
data/                              kernel_oops.txt                    report.txt                         xorg.conf
doc/                               khang                              status.sh                          xserver/
driver/                            lib/                               status2.sh                         
drm/                               mesa/                              util/                              
(gdb) directory ~alex/src/gentoo/
portage/     portage.git/ tmp/         
(gdb) directory ~alex/src/gentoo/tmp/portage/
app-emulation/ dev-libs/      media-sound/   net-im/        net-libs/      net-wireless/  x11-libs/      x11-misc/      
(gdb) directory ~alex/src/gentoo/tmp/portage/x11-libs/libdrm-2.4.6/
.compiled     .exit_status  .unpacked     build-info/   distdir/      homedir/      temp/         work/         
(gdb) directory ~alex/src/gentoo/tmp/portage/x11-libs/libdrm-2.4.6/work/libdrm-2.4.6/
.elibtoolized       README              config.log          configure.ac        libdrm.pc           libtool             tests/              
Makefile            aclocal.m4          config.status       depcomp             libdrm.pc.in        ltmain.sh           
Makefile.am         autom4te.cache/     config.sub          install-sh          libdrm_intel.pc     missing             
Makefile.in         config.guess        configure           libdrm/             libdrm_intel.pc.in  shared-core/        
(gdb) directory ~alex/src/gentoo/tmp/portage/x11-libs/libdrm-2.4.6/work/libdrm-2.4.6/libdrm
libdrm/             libdrm.pc           libdrm.pc.in        libdrm_intel.pc     libdrm_intel.pc.in  
(gdb) directory ~alex/src/gentoo/tmp/portage/x11-libs/libdrm-2.4.6/work/libdrm-2.4.6/libdrm
Source directories searched: /home/alex/src/gentoo/tmp/portage/x11-libs/libdrm-2.4.6/work/libdrm-2.4.6/libdrm:$cdir:$cwd
(gdb) bt
#0  drm_intel_gem_bo_unreference_locked (bo=0x15d6e30) at intel_bufmgr_gem.c:585
#1  0x00007f1e7072b017 in drm_intel_gem_bo_unreference_locked (bo=0x1573b90) at intel_bufmgr_gem.c:561
#2  0x00007f1e7072b4ac in drm_intel_gem_bo_unreference (bo=0x1573b90) at intel_bufmgr_gem.c:599
#3  0x00007f1e7094ebc2 in intel_batch_flush (pScrn=0x1279760, flushed=<value optimized out>) at i830_batchbuffer.c:204
#4  0x00007f1e70959a1e in I830BlockHandler (i=0, blockData=0x0, pTimeout=0x7fff7c3edde8, pReadmask=0x7cb9c0) at i830_driver.c:2656
#5  0x00000000005134f9 in AnimCurScreenBlockHandler (screenNum=0, blockData=0x0, pTimeout=0x7fff7c3edde8, pReadmask=0x7cb9c0) at animcur.c:199
#6  0x00000000004ef931 in compBlockHandler (i=0, blockData=0x0, pTimeout=0x7fff7c3edde8, pReadmask=0x7cb9c0) at compinit.c:163
#7  0x000000000044c08f in BlockHandler (pTimeout=0x7fff7c3edde8, pReadmask=0x7cb9c0) at dixutils.c:383
#8  0x00000000004de78b in WaitForSomething (pClientsReady=0x1574050) at WaitFor.c:223
#9  0x00000000004487fb in Dispatch () at dispatch.c:375
#10 0x0000000000430735 in main (argc=9, argv=0x7fff7c3edfa8, envp=<value optimized out>) at main.c:438
(gdb) frame 0
#0  drm_intel_gem_bo_unreference_locked (bo=0x15d6e30) at intel_bufmgr_gem.c:585
585		    DRMLISTADDTAIL(&bo_gem->head, &bucket->head);
(gdb) l
580		    bo_gem->validate_index = -1;
581		    bo_gem->relocs = NULL;
582		    bo_gem->reloc_target_bo = NULL;
583		    bo_gem->reloc_count = 0;
584	
585		    DRMLISTADDTAIL(&bo_gem->head, &bucket->head);
586		    bucket->num_entries++;
587		} else {
588		    drm_intel_gem_bo_free(bo);
589		}
(gdb)