What driver, dmesg logs, Xorg logs?

xf86-intel-dri, Intel Corporation Haswell-ULT Integrated Graphics Controller
xf86-video-ait, Advanced Micro Devices, Inc. [AMD/ATI] Venus XTX [Radeon HD 8890M / R9 M275X]

dmesg doesn't contain much information:

[ 76.861694] [drm] probing gen 2 caps for device 8086:9c18 = 5323c42/0
[ 76.861699] [drm] PCIE gen 2 link speeds already enabled
[ 76.864492] [drm] PCIE GART of 1024M enabled (table at 0x0000000000276000).
[ 76.864661] radeon 0000:05:00.0: WB enabled
[ 76.864664] radeon 0000:05:00.0: fence driver on ring 0 use gpu addr 0x0000000080000c00 and cpu addr 0xffff880098ebbc00
[ 76.864667] radeon 0000:05:00.0: fence driver on ring 1 use gpu addr 0x0000000080000c04 and cpu addr 0xffff880098ebbc04
[ 76.864669] radeon 0000:05:00.0: fence driver on ring 2 use gpu addr 0x0000000080000c08 and cpu addr 0xffff880098ebbc08
[ 76.864671] radeon 0000:05:00.0: fence driver on ring 3 use gpu addr 0x0000000080000c0c and cpu addr 0xffff880098ebbc0c
[ 76.864673] radeon 0000:05:00.0: fence driver on ring 4 use gpu addr 0x0000000080000c10 and cpu addr 0xffff880098ebbc10
[ 76.866219] radeon 0000:05:00.0: fence driver on ring 5 use gpu addr 0x0000000000075a18 and cpu addr 0xffffc90023235a18
[ 77.458938] [drm] ring test on 0 succeeded in 1 usecs
[ 77.458944] [drm] ring test on 1 succeeded in 1 usecs
[ 77.458949] [drm] ring test on 2 succeeded in 1 usecs
[ 77.458965] [drm] ring test on 3 succeeded in 4 usecs
[ 77.458973] [drm] ring test on 4 succeeded in 1 usecs
[ 77.646218] [drm] ring test on 5 succeeded in 2 usecs
[ 77.646224] [drm] UVD initialized successfully.
[ 77.646258] [drm] ib test on ring 0 succeeded in 0 usecs
[ 77.646290] [drm] ib test on ring 1 succeeded in 0 usecs
[ 77.646320] [drm] ib test on ring 2 succeeded in 0 usecs
[ 77.646350] [drm] ib test on ring 3 succeeded in 0 usecs
[ 77.646380] [drm] ib test on ring 4 succeeded in 0 usecs
[ 77.798250] [drm] ib test on ring 5 succeeded
--------------------here the X crashed--------------------
[ 86.016360] [drm] probing gen 2 caps for device 8086:9c18 = 5323c42/0
[ 86.016370] [drm] PCIE gen 2 link speeds already enabled
[ 86.019255] [drm] PCIE GART of 1024M enabled (table at 0x0000000000276000).
[ 86.019485] radeon 0000:05:00.0: WB enabled
[ 86.019490] radeon 0000:05:00.0: fence driver on ring 0 use gpu addr 0x0000000080000c00 and cpu addr 0xffff880098ebbc00
[ 86.019494] radeon 0000:05:00.0: fence driver on ring 1 use gpu addr 0x0000000080000c04 and cpu addr 0xffff880098ebbc04
[ 86.019497] radeon 0000:05:00.0: fence driver on ring 2 use gpu addr 0x0000000080000c08 and cpu addr 0xffff880098ebbc08
[ 86.019500] radeon 0000:05:00.0: fence driver on ring 3 use gpu addr 0x0000000080000c0c and cpu addr 0xffff880098ebbc0c
[ 86.019503] radeon 0000:05:00.0: fence driver on ring 4 use gpu addr 0x0000000080000c10 and cpu addr 0xffff880098ebbc10
[ 86.021054] radeon 0000:05:00.0: fence driver on ring 5 use gpu addr 0x0000000000075a18 and cpu addr 0xffffc90023235a18
[ 86.612588] [drm] ring test on 0 succeeded in 1 usecs
[ 86.612595] [drm] ring test on 1 succeeded in 1 usecs
[ 86.612600] [drm] ring test on 2 succeeded in 1 usecs
[ 86.612616] [drm] ring test on 3 succeeded in 4 usecs
[ 86.612624] [drm] ring test on 4 succeeded in 1 usecs
[ 86.799870] [drm] ring test on 5 succeeded in 2 usecs
[ 86.799878] [drm] UVD initialized successfully.
[ 86.799914] [drm] ib test on ring 0 succeeded in 0 usecs
[ 86.799946] [drm] ib test on ring 1 succeeded in 0 usecs
[ 86.799976] [drm] ib test on ring 2 succeeded in 0 usecs
[ 86.800007] [drm] ib test on ring 3 succeeded in 0 usecs
[ 86.800037] [drm] ib test on ring 4 succeeded in 0 usecs
[ 86.951900] [drm] ib test on ring 5 succeeded

the dmesg logs before and after crash are the same.

And Xorg logs only mention about this:
[ 61.946] (EE) Backtrace:
[ 61.954] (EE) 0: /usr/bin/Xorg.bin (xorg_backtrace+0x56) [0x593a46]
[ 61.954] (EE) 1: /usr/bin/Xorg.bin (0x400000+0x197b99) [0x597b99]
[ 61.954] (EE) 2: /usr/lib/libc.so.6 (0x7f642b15c000+0x339f0) [0x7f642b18f9f0]
[ 61.954] (EE)
[ 61.954] (EE) Segmentation fault at address 0x0
[ 61.954] (EE)
Fatal server error:
[ 61.954] (EE) Caught signal 11 (Segmentation fault). Server aborting
[ 61.954] (EE)
[ 61.954] (EE)

Can confirm this bug. I have an identical backtrace in the Xorg logs. I too have a Radeon card using the open source drivers, although mine is a 7730M. Here's my lspci:

[thirtythreeforty@laptop ~]$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Chelsea LP [Radeon HD 7730M] (rev ff)

Extremely frustrating... Seems to happen most often with LibreOffice and Mathematica, although Firefox can trigger it too. This bug was present on Linux 3.16.x but has persisted upon upgrade to 3.17.1.

Seems to be xf86-video-ati's problem?

After remove it, everything run just well.

Our graphics cards both seem to be the "muxless hybrid" type. I'm using PRIME to enable this one on demand; most of the time it's not doing anything.

I'd remove the ATI drivers but I'm afraid it would just murder my battery life.

If executed firefox from weston using xWayland, error was in allocating video memory in radeon driver, if executed from X just crash my X server, I'm using xf86-video-ati.
I found this bug while trying to clean cookies in firefox.

I can't reproduce the bug
* firefox-33.1.1-1
* linux-3.17.3-1
* xf86-nouveau-video-1.0.11-2

Is this still valid with current versions of xf86-video-ati and mesa?

No it is not.