Bug 43296

System Environment:
--------------------------
Arch:           i386
Platform:       huronriver
Libdrm:         (master)2.4.27-2-gca4971292cf99e0063416cd1c3467af94637bf2b
Mesa:           (master)d4fcf67a3ac78c29448000486dadc2b4b1b2a56d
Xserver:      
(master)xorg-server-1.11.99.1-43-gb2015a2c01711646bb7ae23d684abee0cd55d4d0
Xf86_video_intel: (master)2.17.0-26-g16f5e224dcfd97012b38ee1af6c72dbe3c0f3304
Kernel:  (drm-intel-next)9a10f401a401ca69c6537641c8fc0d6b57b5aee8


Bug detailed description:
------------------------- 
It segfaults on latest mesa master commit. There are many other oglc cases segfault.  Bisect are blocked by Mesa build failure.
The last known good commit is 0fe14178dbd5b350082a06c7488b6077362a85e3. 
The last known bad commit is 24d25b55bf511493e70600cc7c49c0a0e6fc7a32.
Below are cases segfault:
oglc bitmap-draw(basic.allCases)
oglc feedback(basic.lineLoopRender)
oglc feedback(basic.lineRender)
oglc feedback(basic.lineStripRender)
oglc feedback(basic.pointRender)
oglc feedback(basic.polyFillRender)
oglc feedback(basic.polyLineRender)
oglc feedback(basic.polyPointRender)
oglc feedback(basic.triFanRender)
oglc feedback(basic.triRender)
oglc feedback(basic.triStripRender)
oglc mustpass(basic.feedback)
oglc mustpass(basic.select)
oglc select(basic.line)
oglc select(basic.triStrip)
oglc float-texture(mipmap.manual)

(gdb) bt
#0  0x00000000 in ?? ()
#1  0xb79d78e7 in intel_set_span_functions (intel=0x80c35f8, rb=0x86d14a8) at intel_span.c:455
#2  intel_renderbuffer_map (intel=0x80c35f8, rb=0x86d14a8) at intel_span.c:205
#3  0xb79d7951 in intel_framebuffer_map (intel=0x80c35f8, fb=<value optimized out>) at intel_span.c:240
#4  0xb79d7b1d in intel_span_map_buffers (ctx=0x80c35f8) at intel_span.c:310
#5  intelSpanRenderStart (ctx=0x80c35f8) at intel_span.c:331
#6  0xb7c38fe4 in swrast_render_start (ctx=0x80c35f8, srcx=0, srcy=0, width=512, height=512, destx=0, desty=0, type=6144) at swrast/s_context.h:325
#7  _swrast_CopyPixels (ctx=0x80c35f8, srcx=0, srcy=0, width=512, height=512, destx=0, desty=0, type=6144) at swrast/s_copypix.c:692
#8  0xb7b8dc79 in _mesa_meta_CopyPixels (ctx=0x80c35f8, srcX=0, srcY=0, width=512, height=512, dstX=0, dstY=0, type=6144) at drivers/common/meta.c:1905
#9  0xb79d8a51 in intelCopyPixels (ctx=0x80c35f8, srcx=0, srcy=0, width=512, height=512, destx=0, desty=0, type=6144) at intel_pixel_copy.c:224
#10 0xb7bfe074 in _mesa_CopyPixels (srcx=0, srcy=0, width=512, height=512, type=6144) at main/drawpix.c:208
#11 0x0806bfff in test_mipmap_copypixels ()
#12 0x0806c32b in piglit_display ()
#13 0x0806c993 in display ()
#14 0xb7eec5b6 in ?? () from /usr/lib/libglut.so.3
#15 0xb7ef03f8 in fgEnumWindows () from /usr/lib/libglut.so.3
#16 0xb7eecb13 in glutMainLoopEvent () from /usr/lib/libglut.so.3
#17 0xb7eed395 in glutMainLoop () from /usr/lib/libglut.so.3
#18 0x0806d089 in main ()


Reproduce steps:
----------------
1. start X
2. ./fbo-mipmap-copypix -auto