Additional info:
reporter:       libreport-2.2.2
WARNING: CPU: 0 PID: 56 at drivers/gpu/drm/i915/intel_panel.c:648 pch_enable_backlight+0x1ba/0x1e0 [i915]()
cpu backlight already enabled
Modules linked in: rfcomm fuse ip6t_rpfilter ip6t_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw bnep iTCO_wdt iTCO_vendor_support gpio_ich arc4 x86_pkg_temp_thermal coretemp kvm_intel snd_hda_codec_realtek ath9k snd_hda_codec_generic kvm snd_hda_codec_hdmi ath9k_common snd_hda_intel crct10dif_pclmul crc32_pclmul snd_hda_codec crc32c_intel ath9k_hw snd_hwdep snd_seq ath mac80211 ath3k ghash_clmulni_intel uvcvideo snd_seq_device videobuf2_vmalloc videobuf2_memops videobuf2_core btusb microcode videodev snd_pcm cfg80211 media serio_raw bluetooth i2c_i801 6lowpan_iphc snd_timer snd rfkill shpchp lpc_ich mfd_core soundcore tpm_tis tpm_infineon tpm i2c_designware_platform i2c_designware_core dw_dmac dw_dmac_core binfmt_misc i915 i2c_algo_bit drm_kms_helper drm i2c_core sdhci_acpi video sdhci mmc_core
CPU: 0 PID: 56 Comm: kworker/u4:4 Not tainted 3.14.8-200.fc20.x86_64 #1
Hardware name: Acer Peppy, BIOS          10/29/2013
Workqueue: events_unbound async_run_entry_fn
 0000000000000000 00000000147779ae ffff880071a6b980 ffffffff816f0502
 ffff880071a6b9c8 ffff880071a6b9b8 ffffffff8108a1cd ffff880036be4000
 ffff8800369bb800 000000000000000f 0000000080000000 ffff880036b42310
Call Trace:
 [<ffffffff816f0502>] dump_stack+0x45/0x56
 [<ffffffff8108a1cd>] warn_slowpath_common+0x7d/0xa0
 [<ffffffff8108a24c>] warn_slowpath_fmt+0x5c/0x80
 [<ffffffffa011105a>] pch_enable_backlight+0x1ba/0x1e0 [i915]
 [<ffffffffa0111729>] intel_panel_enable_backlight+0xa9/0xe0 [i915]
 [<ffffffffa01072b5>] ironlake_edp_backlight_on+0xb5/0xd0 [i915]
 [<ffffffffa0100a63>] intel_enable_ddi+0xa3/0xf0 [i915]
 [<ffffffffa00f108b>] haswell_crtc_enable+0x23b/0x620 [i915]
 [<ffffffffa00f24a7>] __intel_set_mode+0x767/0x1610 [i915]
 [<ffffffffa00f8b25>] intel_modeset_setup_hw_state+0xb95/0xc90 [i915]
 [<ffffffffa00ba2c3>] __i915_drm_thaw+0x143/0x200 [i915]
 [<ffffffffa00bac5b>] i915_resume+0x2b/0x50 [i915]
 [<ffffffffa00bac96>] i915_pm_resume+0x16/0x20 [i915]
 [<ffffffff813962d4>] pci_pm_resume+0x64/0xb0
 [<ffffffff81396270>] ? pci_pm_thaw+0xa0/0xa0
 [<ffffffff8146dd59>] dpm_run_callback+0x49/0xa0
 [<ffffffff8146deb6>] device_resume+0xc6/0x1f0
 [<ffffffff8146dffd>] async_resume+0x1d/0x50
 [<ffffffff810b44f9>] async_run_entry_fn+0x39/0x120
 [<ffffffff810a68e6>] process_one_work+0x176/0x430
 [<ffffffff810a757b>] worker_thread+0x11b/0x3a0
 [<ffffffff810a7460>] ? rescuer_thread+0x3b0/0x3b0
 [<ffffffff810ae2d1>] kthread+0xe1/0x100
 [<ffffffff810ae1f0>] ? insert_kthread_work+0x40/0x40
 [<ffffffff8170083c>] ret_from_fork+0x7c/0xb0
 [<ffffffff810ae1f0>] ? insert_kthread_work+0x40/0x40