[  288.752257] BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
[  288.752283] IP: [<ffffffffa027c100>] intel_psr_ready+0x76/0x194 [i915]
[  288.752372] PGD 14633c067 PUD 149b23067 PMD 0 
[  288.752389] Oops: 0000 [#1] SMP 
[  288.752399] Modules linked in: i915 uinput hid_generic usbhid hid loop x86_pkg_temp_thermal coretemp ghash_clmulni_intel aesni_intel aes_x86_64 ablk_helper cryptd lrw gf128mul glue_helper iTCO_wdt iTCO_vendor_support microcode pcspkr i2c_i801 battery xhci_pci xhci_hcd lpc_ich intel_gtt mfd_core usbcore drm_kms_helper usb_common ac acpi_pad acpi_cpufreq evdev processor sd_mod crc32c_intel ahci libahci libata scsi_mod thermal fan
[  288.752548] CPU: 3 PID: 4108 Comm: Xorg Tainted: G        W       4.0.0-rc6+ #199
[  288.752555] Hardware name: Intel Corporation Broadwell Client platform/SawTooth Peak, BIOS BDW-E1R1.86C.0093.R00.1409071941 09/07/2014
[  288.752562] task: ffff8800367ed550 ti: ffff8800ab5dc000 task.ti: ffff8800ab5dc000
[  288.752568] RIP: 0010:[<ffffffffa027c100>]  [<ffffffffa027c100>] intel_psr_ready+0x76/0x194 [i915]
[  288.752637] RSP: 0018:ffff8800ab5dfa98  EFLAGS: 00010286
[  288.752643] RAX: 00000000fffffff9 RBX: ffff8800ab7d0000 RCX: 0000000000000003
[  288.752648] RDX: 0000000000000018 RSI: ffff880036b88c00 RDI: ffff8800a788b0e0
[  288.752654] RBP: ffff8800ab5dfab8 R08: 0000000000000000 R09: 0000000000000000
[  288.752659] R10: 0000000000000780 R11: 00000000000007ae R12: ffff88003548a000
[  288.752664] R13: 0000000000000000 R14: ffff8800a788b0e0 R15: ffff880036b88c00
[  288.752671] FS:  00007f5b6e064880(0000) GS:ffff88014ecc0000(0000) knlGS:0000000000000000
[  288.752677] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  288.752682] CR2: 0000000000000020 CR3: 0000000148a49000 CR4: 00000000003407e0
[  288.752688] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  288.752693] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  288.752697] Stack:
[  288.752702]  ffff8800a788b000 0000000000000018 ffff880146170000 0000000000000000
[  288.752717]  ffff8800ab5dfb58 ffffffffa028be02 0000000000000000 0000000000000000
[  288.752736]  ffff880036b88c18 ffff8800ab7d0000 ffff8800356a8800 ffff8800a788b0e0
[  288.752751] Call Trace:
[  288.752824]  [<ffffffffa028be02>] intel_dp_compute_config+0x1be/0x543 [i915]
[  288.752889]  [<ffffffffa0284fb0>] intel_ddi_compute_config+0x66/0x6f [i915]
[  288.752953]  [<ffffffffa02719f3>] intel_modeset_compute_config+0x737/0xd79 [i915]
[  288.753011]  [<ffffffffa02747c4>] intel_crtc_set_config+0x830/0xc98 [i915]
[  288.753024]  [<ffffffff812a7110>] ? _object_find+0x56/0x7a
[  288.753033]  [<ffffffff812a7d8d>] drm_mode_set_config_internal+0x55/0xe2
[  288.753042]  [<ffffffff812abca9>] drm_mode_setcrtc+0x448/0x4dd
[  288.753052]  [<ffffffff812a040e>] drm_ioctl+0x27c/0x3da
[  288.753061]  [<ffffffff81140615>] ? fsnotify+0x26d/0x293
[  288.753070]  [<ffffffff812ab861>] ? drm_mode_setplane+0x1c3/0x1c3
[  288.753080]  [<ffffffff81120bb5>] do_vfs_ioctl+0x419/0x461
[  288.753090]  [<ffffffff81112dbb>] ? fdput.isra.9+0xf/0x11
[  288.753099]  [<ffffffff81112de6>] ? fdput_pos.isra.10+0x29/0x30
[  288.753107]  [<ffffffff81128534>] ? __fget+0x20/0x5a
[  288.753115]  [<ffffffff81120c36>] SyS_ioctl+0x39/0x63
[  288.753125]  [<ffffffff813998b2>] system_call_fastpath+0x12/0x17
[  288.753130] Code: e9 2b 01 00 00 41 8b 84 24 28 02 00 00 ff c8 75 1a 48 c7 c2 54 4b 2c a0 be 18 01 00 00 48 c7 c7 a2 4a 2c a0 31 c0 e8 79 f0 db e0 <41> 8b 45 20 ff c8 75 1a 48 c7 c2 98 4b 2c a0 be 19 01 00 00 48 
[  288.753309] RIP  [<ffffffffa027c100>] intel_psr_ready+0x76/0x194 [i915]
[  288.753384]  RSP <ffff8800ab5dfa98>
[  288.753390] CR2: 0000000000000020


(gdb) list *intel_psr_ready+0x76
0x61124 is in intel_psr_ready (./arch/x86/include/asm/atomic.h:27).
22	 *
23	 * Atomically reads the value of @v.
24	 */
25	static inline int atomic_read(const atomic_t *v)
26	{
27		return ACCESS_ONCE((v)->counter);
28	}
29	
30	/**
31	 * atomic_set - set atomic variable