Comment 19 for bug 1542939

I confirm this bug. Sometimes, Xserver hangs when switching back VT from text mode to graphical display. When it hangs, suspend2ram and resume fixes the issue. Here is the stack :

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WARNING: CPU: 2 PID: 10921 at drivers/gpu/drm/drm_irq.c:1326 drm_wait_one_vblank+0x1b0/0x1c0 [drm]()
vblank wait timed out on crtc 0
Modules linked in: sha256_ssse3 sha256_generic hmac drbg ansi_cprng ctr ccm joydev mousedev iTCO_wdt i
 syscopyarea mei sysfillrect sysimgblt fb_sys_fops i2c_algo_bit snd_timer ptp pps_core nvram snd sound
CPU: 2 PID: 10921 Comm: Xorg Tainted: G U W O 4.4.5-1-ARCH #1
Hardware name: LENOVO 4236JZ5/4236JZ5, BIOS 83ET78WW (1.48 ) 01/21/2016
 0000000000000286 0000000074de7b7f ffff8800c2edf810 ffffffff812cb391
 ffff8800c2edf858 ffffffffa0533272 ffff8800c2edf848 ffffffff810776e2
 ffff880118b99800 0000000000000000 0000000000000000 00000000000ac2c4
Call Trace:
 [<ffffffff812cb391>] dump_stack+0x63/0x82
 [<ffffffff810776e2>] warn_slowpath_common+0x82/0xc0
 [<ffffffff8107777c>] warn_slowpath_fmt+0x5c/0x80
 [<ffffffff810b8825>] ? finish_wait+0x55/0x70
 [<ffffffff810747eb>] ? __mmdrop+0x7b/0xd0
 [<ffffffffa0506840>] drm_wait_one_vblank+0x1b0/0x1c0 [drm]
 [<ffffffff810b8cc0>] ? wake_atomic_t_function+0x60/0x60
 [<ffffffffa0791685>] intel_atomic_commit+0x475/0x1430 [i915]
 [<ffffffffa051f55e>] ? drm_atomic_check_only+0x18e/0x590 [drm]
 [<ffffffffa051f307>] ? drm_atomic_add_affected_connectors+0x27/0xf0 [drm]
 [<ffffffffa051f997>] drm_atomic_commit+0x37/0x60 [drm]
 [<ffffffffa0572faf>] restore_fbdev_mode+0x22f/0x260 [drm_kms_helper]
 [<ffffffffa0575313>] drm_fb_helper_restore_fbdev_mode_unlocked+0x33/0x80 [drm_kms_helper]
 [<ffffffffa057538d>] drm_fb_helper_set_par+0x2d/0x50 [drm_kms_helper]
 [<ffffffffa07a819a>] intel_fbdev_set_par+0x1a/0x60 [i915]
 [<ffffffff812f2db9>] ? __percpu_counter_add+0x59/0x80
 [<ffffffff8133fa46>] fb_set_var+0x236/0x460
 [<ffffffff8117db21>] ? shmem_recalc_inode+0x71/0xa0
 [<ffffffff810a744c>] ? __enqueue_entity+0x6c/0x70
 [<ffffffff810adfeb>] ? enqueue_entity+0x1fb/0xd20
 [<ffffffff813366ef>] fbcon_blank+0x30f/0x350
 [<ffffffff813b2ef3>] do_unblank_screen+0xc3/0x190
 [<ffffffff813a941a>] vt_ioctl+0x50a/0x12e0
 [<ffffffff811f0050>] ? filename_parentat+0xe0/0x150
 [<ffffffff8139d731>] tty_ioctl+0x361/0xc30
 [<ffffffff813e5693>] ? vga_arb_release+0xe3/0x130
 [<ffffffff811c33d0>] ? kfree+0x170/0x180
 [<ffffffff811fff5c>] ? mntput_no_expire+0x2c/0x1b0
 [<ffffffff811f3258>] do_vfs_ioctl+0x298/0x480
 [<ffffffff811fd307>] ? __fget+0x77/0xb0
 [<ffffffff811f34b9>] SyS_ioctl+0x79/0x90
 [<ffffffff815970ee>] entry_SYSCALL_64_fastpath+0x12/0x6d
---[ end trace 5926662876f4c875 ]---