Oh right, I had noticed that the gpu threads are segfaulting, but totally forgot that it could be relevant here.

Ivy Bridge here:

Core was generated by `/opt/google/chrome-unstable/chrome --type=gpu-process --channel=21942.4.5215851'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f84164044b8 in get_stencil_miptree (irb=0xf09fc2270b0) at brw_misc_state.c:225
225        if (irb->mt->stencil_mt)
(gdb) bt full
#0  0x00007f84164044b8 in get_stencil_miptree (irb=0xf09fc2270b0) at brw_misc_state.c:225                                                                                                                                                                                                                       
No locals.                                                                                                                                                                                                                                                                                                      
#1  0x00007f8416404551 in brw_workaround_depthstencil_alignment (brw=0xf09fd940030, clear_mask=50) at brw_misc_state.c:241                                                                                                                                                                                      
        ctx = 0xf09fd940030                                                                                                                                                                                                                                                                                     
        fb = 0xf09fea11200                                                                                                                                                                                                                                                                                      
        rebase_depth = false                                                                                                                                                                                                                                                                                    
        rebase_stencil = false                                                                                                                                                                                                                                                                                  
        depth_irb = 0xf09fc22af20                                                                                                                                                                                                                                                                               
        stencil_irb = 0xf09fc2270b0                                                                                                                                                                                                                                                                             
        depth_mt = 0x0                                                                                                                                                                                                                                                                                          
        stencil_mt = 0xf09fd9717c0                                                                                                                                                                                                                                                                              
        tile_x = 32767                                                                                                                                                                                                                                                                                          
        tile_y = 2049073776                                                                                                                                                                                                                                                                                     
        stencil_tile_x = 3849                                                                                                                                                                                                                                                                                   
        stencil_tile_y = 4254335024                                                                                                                                                                                                                                                                             
        stencil_draw_x = 4271968768                                                                                                                                                                                                                                                                             
        stencil_draw_y = 3849                                                                                                                                                                                                                                                                                   
        invalidate_depth = 255                                                                                                                                                                                                                                                                                  
        invalidate_stencil = false                                                                                                                                                                                                                                                                              
        tile_mask_x = 4254335024                                                                                                                                                                                                                                                                                
        tile_mask_y = 3849                                                                                                                                                                                                                                                                                      
#2  0x00007f84163a6ff3 in brw_clear (ctx=0xf09fd940030, mask=50) at brw_clear.c:235                                                                                                                                                                                                                             
        brw = 0xf09fd940030                                                                                                                                                                                                                                                                                     
        fb = 0xf09fea11200                                                                                                                                                                                                                                                                                      
        partial_clear = false                                                                                                                                                                                                                                                                                   
        tri_mask = 4254335024                                                                                                                                                                                                                                                                                   
#3  0x00007f841603028b in _mesa_Clear (mask=17664) at ../../src/mesa/main/clear.c:226                                                                                                                                                                                                                           
        bufferMask = 50                                                                                                                                                                                                                                                                                         
        ctx = 0xf09fd940030                                                                                                                                                                                                                                                                                     
        __func__ = "_mesa_Clear"                                                                                                                                                                                                                                                                                
        __PRETTY_FUNCTION__ = "_mesa_Clear"                                                                                                                                                                                                                                                                     
#4  0x00007f842933836a in ?? ()                                                                                                                                                                                                                                                                                 
No symbol table info available.                                                                                                                                                                                                                                                                                 
#5  0x0000000000000000 in ?? ()                                                                                                                                                                                                                                                                                 
No symbol table info available.