This crash occured after about a day with 3.18.0-rc3 that is unmodified with exception of a single unrelated i915 driver patch from http://www.spinics.net/lists/intel-gfx/msg54997.html
Its a samsung np730u3e-s05 with hybrid graphics chipset and the Radeon HD 8550M isn't used. I can provide further info if this is of interest.
[23168.559229] BUG: unable to handle kernel NULL pointer dereference at 0000000000000018 [23168.560206] IP: [<ffffffffa0458700>] ttm_dma_unpopulate+0x260/0x390 [ttm] [23168.561209] PGD 0 [23168.562145] Oops: 0000 [#1] PREEMPT SMP [23168.563096] Modules linked in: ctr ccm fuse arc4 snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic iTCO_wdt uvcvideo iwldvm coretemp videobuf2_vmalloc intel_rapl joydev videobuf2_memops mac80211 videobuf2_core snd_hda_intel snd_hda_controller iTCO_vendor_support mousedev x86_pkg_temp_thermal intel_powerclamp radeon v4l2_common iwlwifi samsung_laptop kvm_intel videodev snd_hda_codec i915 ttm evdev ecb mac_hid snd_hwdep drm_kms_helper r8169 kvm btusb psmouse pcspkr serio_raw i2c_i801 media cfg80211 drm lpc_ich rtsx_usb_ms intel_gtt snd_pcm hwmon bluetooth mii i2c_algo_bit tpm_infineon memstick mei_me fan rfkill snd_timer wmi tpm_tis i2c_core battery snd thermal tpm soundcore mei video shpchp button ac processor ext4 crc16 mbcache jbd2 algif_skcipher af_alg dm_crypt dm_mod rtsx_usb_sdmmc [23168.566629] led_class mmc_core rtsx_usb sd_mod crct10dif_pclmul crc32_pclmul crc32c_intel atkbd ghash_clmulni_intel libps2 aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd ahci libahci xhci_pci ehci_pci libata xhci_hcd ehci_hcd scsi_mod usbcore usb_common i8042 serio [23168.569111] CPU: 3 PID: 406 Comm: Xorg.bin Tainted: G W 3.18.0-rc3-marcus1 #1 [23168.570348] Hardware name: SAMSUNG ELECTRONICS CO., LTD. 730U3E/740U3E/NP730U3E-S05DE, BIOS P03ABW.051.130226.dg 02/26/2013 [23168.571614] task: ffff8801a5cf6eb0 ti: ffff8800bf908000 task.ti: ffff8800bf908000 [23168.572879] RIP: 0010:[<ffffffffa0458700>] [<ffffffffa0458700>] ttm_dma_unpopulate+0x260/0x390 [ttm] [23168.574163] RSP: 0000:ffff8800bf90b978 EFLAGS: 00010207 [23168.575443] RAX: 0000000000000000 RBX: ffff8801a55d6300 RCX: 0000000000000005 [23168.576719] RDX: ffff8800bffd3600 RSI: dead000000200200 RDI: ffff8801a55d6900 [23168.578039] RBP: ffff8800bf90b9b8 R08: 0000000000000004 R09: ffff8800c372b5a0 [23168.579310] R10: 0000000000000000 R11: 0000000000000001 R12: ffff8801a55d6360 [23168.580579] R13: ffff8801a4bd4710 R14: ffff8801a4f3cb40 R15: 0000000000000006 [23168.581855] FS: 00007fd27407f700(0000) GS:ffff8801af380000(0000) knlGS:0000000000000000 [23168.583145] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [23168.584434] CR2: 0000000000000018 CR3: 0000000001811000 CR4: 00000000001407e0 [23168.585742] Stack: [23168.587045] ffff8800c3728800 ffff8801a55d6900 ffff8801a4bd4000 ffff8801a55d6300 [23168.588420] 0000000000000002 ffff8801a4bd4710 ffff8801a55d6300 000000000000002a [23168.589785] ffff8800bf90b9e8 ffffffffa094a8b7 ffff8801a55d6300 0000000000000002 [23168.591134] Call Trace: [23168.592483] [<ffffffffa094a8b7>] radeon_ttm_tt_unpopulate+0x147/0x150 [radeon] [23168.593878] [<ffffffffa044f2a4>] ttm_tt_unpopulate+0x54/0x60 [ttm] [23168.595220] [<ffffffffa044f315>] ttm_tt_destroy+0x65/0x70 [ttm] [23168.596557] [<ffffffffa044fa93>] ttm_bo_cleanup_memtype_use+0x43/0x90 [ttm] [23168.597901] [<ffffffffa0450730>] ttm_bo_release+0x120/0x2e0 [ttm] [23168.599188] [<ffffffffa0450919>] ttm_bo_unref+0x29/0x30 [ttm] [23168.600431] [<ffffffffa094c2f9>] radeon_bo_unref+0x39/0x70 [radeon] [23168.601661] [<ffffffffa096137b>] radeon_gem_object_free+0x4b/0x70 [radeon] [23168.602899] [<ffffffffa049dbf7>] drm_gem_object_free+0x27/0x40 [drm] [23168.604143] [<ffffffffa049dd30>] drm_gem_object_handle_unreference_unlocked+0x120/0x130 [drm] [23168.605406] [<ffffffffa049df77>] drm_gem_object_release_handle+0x57/0x80 [drm] [23168.606668] [<ffffffff812ad2e5>] idr_for_each+0xb5/0x120 [23168.607934] [<ffffffffa049df20>] ? drm_gem_dumb_destroy+0x20/0x20 [drm] [23168.609213] [<ffffffffa049e5f4>] drm_gem_release+0x24/0x40 [drm] [23168.610463] [<ffffffffa049d35b>] drm_release+0x43b/0x520 [drm] [23168.611773] [<ffffffff811c9b8c>] __fput+0x9c/0x200 [23168.613039] [<ffffffff811c9d3e>] ____fput+0xe/0x10 [23168.614333] [<ffffffff8108834c>] task_work_run+0xbc/0xe0 [23168.615577] [<ffffffff8106e505>] do_exit+0x3a5/0xb30 [23168.616825] [<ffffffff8109123e>] ? ttwu_stat+0x9e/0x110 [23168.618083] [<ffffffff810e5e60>] ? get_futex_key+0x250/0x2c0 [23168.619400] [<ffffffff8106ed27>] do_group_exit+0x47/0xc0 [23168.620666] [<ffffffff8107a673>] get_signal+0x273/0x710 [23168.621931] [<ffffffff810145f7>] do_signal+0x37/0x800 [23168.623221] [<ffffffff81014e28>] do_notify_resume+0x68/0xa0 [23168.624488] [<ffffffff8154d1e0>] int_signal+0x12/0x17 [23168.625762] Code: ff 66 2e 0f 1f 84 00 00 00 00 00 49 89 ce 48 8b 43 60 4c 8d 63 60 45 31 ff 4c 39 e0 74 28 45 31 ff 66 2e 0f 1f 84 00 00 00 00 00 <48> 8b 70 18 48 8b 53 18 44 89 f9 41 83 c7 01 48 89 34 ca 48 8b [23168.627274] RIP [<ffffffffa0458700>] ttm_dma_unpopulate+0x260/0x390 [ttm] [23168.628790] RSP <ffff8800bf90b978> [23168.630300] CR2: 0000000000000018 [23168.631810] ---[ end trace acd63743d38c53a7 ]--- [23168.633307] Fixing recursive fault but reboot is needed!
regards Marcus