I tested the upstream kernel on my current Ubuntu 14.04 installation, but still get the same issues.
linux-image-3.19.0-031900rc6

The following packages were used:
linux-image-3.19.0-031900rc6-generic_3.19.0-031900rc6.201501261152_amd64.deb
linux-headers-3.19.0-031900rc6_3.19.0-031900rc6.201501261152_all.deb
linux-headers-3.19.0-031900rc6-generic_3.19.0-031900rc6.201501261152_amd64.deb

from this location: http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.19-rc6-vivid/

I also installed a new linux-firmware package, because otherwise the kernel installation would log some warnings about missing firmeware files for the radeon module.

I used the package from 14.10: http://packages.ubuntu.com/utopic/linux-firmware
linux-firmware_1.138_all.deb


This is the first stack trace I get:

[   20.620150] WARNING: CPU: 2 PID: 154 at /home/kernel/COD/linux/drivers/gpu/drm/radeon/radeon_gart.c:234 radeon_gart_unbind+0xda/0xf0 [radeon]()
[   20.620151] trying to unbind memory from uninitialized GART !
[   20.620152] Modules linked in: ctr ccm arc4 brcmsmac rfcomm bnep cordic bluetooth brcmutil b43 mac80211 intel_powerclamp coretemp kvm_intel cfg80211 ssb kvm snd_seq_midi binfmt_misc uvcvideo snd_hda_codec_realtek snd_seq_midi_event snd_hda_codec_generic crct10dif_pclmul snd_hda_codec_hdmi snd_rawmidi videobuf2_vmalloc videobuf2_memops crc32_pclmul videobuf2_core ghash_clmulni_intel v4l2_common videodev acer_wmi sparse_keymap snd_hda_intel snd_hda_controller aesni_intel snd_hda_codec snd_hwdep media aes_x86_64 lrw snd_pcm gf128mul glue_helper joydev ablk_helper cryptd snd_seq snd_seq_device snd_timer serio_raw intel_ips snd mei_me bcma soundcore parport_pc mei lpc_ich ppdev mac_hid lp parport amdkfd amd_iommu_v2 radeon i915 psmouse ttm i2c_algo_bit ahci drm_kms_helper libahci drm atl1c wmi video
[   20.620185] CPU: 2 PID: 154 Comm: kworker/u16:5 Not tainted 3.19.0-031900rc6-generic #201501261152
[   20.620186] Hardware name: Acer /JM41_CP, BIOS V1.25 03/16/2011
[   20.620193] Workqueue: kacpi_hotplug acpi_hotplug_work_fn
[   20.620194]  00000000000000ea ffff8801312af6f8 ffffffff817c4584 0000000000000007
[   20.620196]  ffff8801312af748 ffff8801312af738 ffffffff81076df7 ffffffff8141e130
[   20.620198]  ffff880036098000 ffff8801312af948 ffff880036098728 ffff8800ad234f00
[   20.620200] Call Trace:
[   20.620206]  [<ffffffff817c4584>] dump_stack+0x45/0x57
[   20.620211]  [<ffffffff81076df7>] warn_slowpath_common+0x97/0xe0
[   20.620215]  [<ffffffff8141e130>] ? update_attr.isra.2+0xa0/0xa0
[   20.620217]  [<ffffffff81076ef6>] warn_slowpath_fmt+0x46/0x50
[   20.620225]  [<ffffffff814aa454>] ? vt_console_print+0x2d4/0x3b0
[   20.620235]  [<ffffffffc065053a>] radeon_gart_unbind+0xda/0xf0 [radeon]
[   20.620245]  [<ffffffffc064cbf2>] radeon_ttm_backend_unbind+0x22/0x40 [radeon]
[   20.620250]  [<ffffffffc0495177>] ttm_tt_unbind+0x27/0x40 [ttm]
[   20.620255]  [<ffffffffc0499b68>] ttm_bo_move_ttm+0xf8/0x130 [ttm]
[   20.620259]  [<ffffffffc0497326>] ttm_bo_handle_move_mem+0x636/0x6f0 [ttm]
[   20.620262]  [<ffffffff810cc888>] ? console_unlock+0x18/0x30
[   20.620263]  [<ffffffff810cd1ae>] ? vprintk_emit+0x25e/0x510
[   20.620266]  [<ffffffff810ddb5c>] ? internal_add_timer+0x6c/0x90
[   20.620270]  [<ffffffffc0497522>] ttm_bo_evict+0x142/0x200 [ttm]
[   20.620274]  [<ffffffffc049776b>] ttm_mem_evict_first+0x18b/0x1f0 [ttm]
[   20.620279]  [<ffffffffc049d4b3>] ? ttm_bo_man_takedown+0x53/0x80 [ttm]
[   20.620283]  [<ffffffffc0497841>] ttm_bo_force_list_clean+0x71/0xc0 [ttm]
[   20.620287]  [<ffffffffc0497937>] ttm_bo_clean_mm+0x47/0x90 [ttm]
[   20.620297]  [<ffffffffc064e6b5>] radeon_ttm_fini+0xf5/0x1c0 [radeon]
[   20.620307]  [<ffffffffc064f436>] radeon_bo_fini+0x16/0x30 [radeon]
[   20.620323]  [<ffffffffc06abd8f>] evergreen_fini+0xaf/0xe0 [radeon]
[   20.620331]  [<ffffffffc063244f>] radeon_device_fini+0x3f/0x140 [radeon]
[   20.620339]  [<ffffffffc0634929>] radeon_driver_unload_kms+0x59/0x80 [radeon]
[   20.620351]  [<ffffffffc03d752d>] drm_dev_unregister+0x2d/0xc0 [drm]
[   20.620358]  [<ffffffffc03d7b07>] drm_put_dev+0x27/0x70 [drm]
[   20.620365]  [<ffffffffc0630215>] radeon_pci_remove+0x15/0x20 [radeon]
[   20.620368]  [<ffffffff813f0cb6>] pci_device_remove+0x46/0xc0
[   20.620371]  [<ffffffff814f687f>] __device_release_driver+0x7f/0xf0
[   20.620373]  [<ffffffff814f691c>] device_release_driver+0x2c/0x40
[   20.620376]  [<ffffffff813eaa9c>] pci_stop_bus_device+0x9c/0xb0
[   20.620377]  [<ffffffff813eaa43>] pci_stop_bus_device+0x43/0xb0
[   20.620379]  [<ffffffff813eac56>] pci_stop_and_remove_bus_device+0x16/0x30
[   20.620382]  [<ffffffff8140a097>] disable_slot+0x57/0xa0
[   20.620384]  [<ffffffff8140a868>] acpiphp_check_bridge.part.11+0xe8/0x100
[   20.620386]  [<ffffffff8140b298>] acpiphp_check_host_bridge+0x88/0xb0
[   20.620389]  [<ffffffff8143c3ba>] acpi_pci_root_scan_dependent+0xe/0x12
[   20.620392]  [<ffffffff81438fcb>] acpi_scan_bus_check+0x48/0xad
[   20.620393]  [<ffffffff81439103>] acpi_generic_hotplug_event+0x2e/0x87
[   20.620395]  [<ffffffff814391b1>] acpi_device_hotplug+0x55/0xcd
[   20.620397]  [<ffffffff814326de>] acpi_hotplug_work_fn+0x20/0x2d
[   20.620401]  [<ffffffff8108f6dd>] process_one_work+0x14d/0x460
[   20.620403]  [<ffffffff810900bb>] worker_thread+0x11b/0x3f0
[   20.620405]  [<ffffffff8108ffa0>] ? create_worker+0x1e0/0x1e0
[   20.620408]  [<ffffffff81095cc9>] kthread+0xc9/0xe0
[   20.620409]  [<ffffffff81095c00>] ? flush_kthread_worker+0x90/0x90
[   20.620412]  [<ffffffff817d17fc>] ret_from_fork+0x7c/0xb0
[   20.620414]  [<ffffffff81095c00>] ? flush_kthread_worker+0x90/0x90
[   20.620415] ---[ end trace 47f988208d7a516b ]---