The previous snippet was from rc8, same behaviour on 4.2.0 tho:

[   25.866954] ------------[ cut here ]------------
[   25.866970] WARNING: CPU: 2 PID: 1030 at /home/kernel/COD/linux/drivers/gpu/drm/i915/intel_display.c:1362 assert_plane.constprop.94+0x73/0xa0 [i915]()
[   25.866971] plane A assertion failure (expected on, current off)
[   25.866991] Modules linked in: xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 xt_tcpudp bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tables x_tables cmac rfcomm bnep uas nls_iso8859_1 usb_storage input_leds joydev uvcvideo videobuf2_vmalloc hid_generic videobuf2_memops videobuf2_core v4l2_common videodev btusb snd_usb_audio btrtl usbhid btbcm media snd_usbmidi_lib btintel bluetooth arc4 intel_rapl iosf_mbi x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm iwlmvm crct10dif_pclmul mac80211 crc32_pclmul ghash_clmulni_intel snd_hda_codec_realtek snd_hda_codec_hdmi snd_soc_rt5640 snd_hda_codec_generic aesni_intel snd_soc_rl6231
[   25.867011]  snd_soc_core aes_x86_64 lrw snd_compress iwlwifi ac97_bus gf128mul snd_pcm_dmaengine glue_helper ablk_helper snd_hda_intel snd_seq_midi cryptd snd_hda_codec snd_seq_midi_event snd_hda_core snd_hwdep cfg80211 serio_raw snd_pcm lpc_ich mei_me shpchp snd_rawmidi mei snd_seq snd_seq_device snd_timer nuvoton_cir rc_core snd i2c_hid hid dw_dmac dw_dmac_core snd_soc_sst_acpi soundcore i2c_designware_platform acpi_als 8250_dw i2c_designware_core kfifo_buf spi_pxa2xx_platform acpi_pad industrialio mac_hid parport_pc ppdev lp parport sunrpc autofs4 raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq raid1 raid0 multipath linear i915 i2c_algo_bit psmouse drm_kms_helper e1000e drm ahci libahci ptp pps_core sdhci_acpi video sdhci
[   25.867012] CPU: 2 PID: 1030 Comm: Xorg Not tainted 4.2.0-040200-generic #201508301530
[   25.867013] Hardware name: \xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff \xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff\xffffffff/NUC5i7RYB, BIOS RYBDWi35.86A.0246.2015.0309.1355 03/09/2015
[   25.867014]  ffffffffc025bc48 ffff880408f237b8 ffffffff817a1b43 0000000000000001
[   25.867015]  ffff880408f23808 ffff880408f237f8 ffffffff8107719a ffff880035e00000
[   25.867016]  0000000000000000 ffff880035e00000 ffff88040c393800 ffff88040c393860
[   25.867016] Call Trace:
[   25.867020]  [<ffffffff817a1b43>] dump_stack+0x45/0x57
[   25.867022]  [<ffffffff8107719a>] warn_slowpath_common+0x8a/0xc0
[   25.867023]  [<ffffffff81077216>] warn_slowpath_fmt+0x46/0x50
[   25.867034]  [<ffffffffc01f29e3>] assert_plane.constprop.94+0x73/0xa0 [i915]
[   25.867043]  [<ffffffffc01fc9e1>] hsw_disable_ips+0x41/0x180 [i915]
[   25.867051]  [<ffffffffc01fcb7d>] intel_pre_disable_primary+0x5d/0x90 [i915]
[   25.867059]  [<ffffffffc01fcbf8>] intel_crtc_disable_planes+0x48/0x110 [i915]
[   25.867067]  [<ffffffffc01fd541>] __intel_set_mode+0x251/0xb10 [i915]
[   25.867075]  [<ffffffffc01ff0b2>] ? intel_modeset_compute_config+0x362/0xb60 [i915]
[   25.867083]  [<ffffffffc0204886>] intel_crtc_set_config+0x366/0x5a0 [i915]
[   25.867092]  [<ffffffffc00803e8>] drm_mode_set_config_internal+0x68/0x100 [drm]
[   25.867095]  [<ffffffffc013ee42>] restore_fbdev_mode+0xc2/0xf0 [drm_kms_helper]
[   25.867098]  [<ffffffffc0140c19>] drm_fb_helper_restore_fbdev_mode_unlocked+0x29/0x70 [drm_kms_helper]
[   25.867101]  [<ffffffffc0140c82>] drm_fb_helper_set_par+0x22/0x40 [drm_kms_helper]
[   25.867109]  [<ffffffffc0211a3a>] intel_fbdev_set_par+0x1a/0x60 [i915]
[   25.867112]  [<ffffffff812bad66>] ? jbd2_journal_dirty_metadata+0xb6/0x250
[   25.867114]  [<ffffffff81413a71>] fb_set_var+0x191/0x400
[   25.867115]  [<ffffffff8129fa01>] ? __ext4_handle_dirty_metadata+0x81/0x210
[   25.867117]  [<ffffffff8140adcc>] fbcon_blank+0x1bc/0x2b0
[   25.867119]  [<ffffffff8149a3d8>] do_unblank_screen+0xb8/0x1c0
[   25.867121]  [<ffffffff814918b3>] vt_ioctl+0x1063/0x10e0
[   25.867123]  [<ffffffff8179e7a8>] ? __slab_free+0x104/0x25c
[   25.867125]  [<ffffffff814847a7>] tty_ioctl+0x1f7/0xbe0
[   25.867127]  [<ffffffff81198671>] ? kzfree+0x31/0x40
[   25.867128]  [<ffffffff811cbc58>] ? kfree+0xf8/0x130
[   25.867130]  [<ffffffff811fc62d>] do_vfs_ioctl+0x2cd/0x4b0
[   25.867131]  [<ffffffff81208df4>] ? mntput+0x24/0x40
[   25.867133]  [<ffffffff811eb4d0>] ? __fput+0x190/0x210
[   25.867134]  [<ffffffff811fc889>] SyS_ioctl+0x79/0x90
[   25.867135]  [<ffffffff817a8e32>] entry_SYSCALL_64_fastpath+0x16/0x75
[   25.867136] ---[ end trace c6b6cf80ff58f9ce ]---

Please try latest v4.3-rc kernel. If the problem persists, please add drm.debug=14 module parameter, and attach dmesg.

*** Bug 106401 has been marked as a duplicate of this bug. ***

Created attachment 190721 [details]
dmesg-4.3.0-0.rc6

Adding the output from DMESG in rc6 if it helps

In my case the call traces are gone in 4.3.0-0.rc6 but instead I'm seeing a bunch of "[drm:gen8_irq_handler [i915]] *ERROR* The master control interrupt lied (SDE)!" in the debug output

Created attachment 190731 [details]
more *ERROR* The master control interrupt lied (SDE)!

moar *ERROR* The master control interrupt lied (SDE)! when screen is locked in Gnome and the monitors power off in the process and awake on keyboard input.

Both monitors turn on with 4.3.0-0.rc6 on bootup and after locked screen as well as switching between tty which did not happen with kernel-4.2.3-300 where it was random if both monitors turned on or only one or none.

(In reply to Jóhann B. Guðmundsson from comment #5)
> In my case the call traces are gone in 4.3.0-0.rc6 but instead I'm seeing a

Thanks, I trust this is fixed for the rest of you as well, closing.

> bunch of "[drm:gen8_irq_handler [i915]] *ERROR* The master control interrupt
> lied (SDE)!" in the debug output

That's a separate bug, tracked at https://bugs.freedesktop.org/show_bug.cgi?id=92084

If new issues arise, please file them at the freedesktop.org bugzilla
https://bugs.freedesktop.org/enter_bug.cgi?product=DRI&component=DRM/Intel