On CI_DRM_3051, the machine fi-gdg-551 hit the following WARNING when running igt@drv_module_reload@basic-reload:

[  269.687157] ------------[ cut here ]------------
[  269.687200] WARNING: CPU: 0 PID: 2481 at drivers/gpu/drm/drm_mode_config.c:465 drm_mode_config_cleanup+0x250/0x270
[  269.687204] Modules linked in: vgem i915(-) intel_powerclamp lpc_ich tg3 ptp pps_core prime_numbers [last unloaded: vgem]
[  269.687247] CPU: 0 PID: 2481 Comm: drv_module_relo Tainted: G     U          4.13.0-CI-CI_DRM_3051+ #1
[  269.687250] Hardware name: Dell Inc.                 OptiPlex GX280               /0G8310, BIOS A04 02/09/2005
[  269.687255] task: ffff880038dccd40 task.stack: ffffc900002b8000
[  269.687260] RIP: 0010:drm_mode_config_cleanup+0x250/0x270
[  269.687264] RSP: 0018:ffffc900002bbd80 EFLAGS: 00010283
[  269.687272] RAX: ffff880038dc1de0 RBX: ffff88002fcd0890 RCX: 0000000000000001
[  269.687275] RDX: ffff88002fcd08b8 RSI: 0000000000000000 RDI: ffff88002fcd0890
[  269.687279] RBP: ffffc900002bbda8 R08: 0000000000000000 R09: 0000000000000000
[  269.687283] R10: ffffc900002bbd00 R11: 0000000000000000 R12: ffff88002fcd0000
[  269.687287] R13: ffff88002fcd06a8 R14: ffffffffa01b6d88 R15: ffff88003d20a5a8
[  269.687291] FS:  00007fd157fed8c0(0000) GS:ffff88003f400000(0000) knlGS:0000000000000000
[  269.687296] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  269.687300] CR2: 000055fa43fc5fe7 CR3: 000000003079c000 CR4: 00000000000006f0
[  269.687304] Call Trace:
[  269.687392]  intel_modeset_cleanup+0x66/0xa0 [i915]
[  269.687431]  i915_driver_unload+0x92/0x180 [i915]
[  269.687472]  i915_pci_remove+0x19/0x30 [i915]
[  269.687480]  pci_device_remove+0x39/0xb0
[  269.687488]  device_release_driver_internal+0x15d/0x220
[  269.687495]  driver_detach+0x40/0x80
[  269.687502]  bus_remove_driver+0x58/0xd0
[  269.687508]  driver_unregister+0x2c/0x40
[  269.687514]  pci_unregister_driver+0x36/0xb0
[  269.687569]  i915_exit+0x1a/0x8b [i915]
[  269.687579]  SyS_delete_module+0x18c/0x1e0
[  269.687588]  entry_SYSCALL_64_fastpath+0x1c/0xb1
[  269.687593] RIP: 0033:0x7fd156505287
[  269.687597] RSP: 002b:00007ffc40d807b8 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
[  269.687605] RAX: ffffffffffffffda RBX: ffffffff8148a693 RCX: 00007fd156505287
[  269.687609] RDX: 0000000000000001 RSI: 0000000000000800 RDI: 000055edd5823008
[  269.687613] RBP: ffffc900002bbf88 R08: 0000000000000000 R09: 0000000000000080
[  269.687616] R10: 0000000000000885 R11: 0000000000000206 R12: 0000000000000000
[  269.687620] R13: 00007ffc40d809a0 R14: 0000000000000000 R15: 0000000000000000
[  269.687628]  ? __this_cpu_preempt_check+0x13/0x20
[  269.687638] Code: da 31 f6 48 c7 c7 73 d9 c7 81 e8 ac 5f fe ff 48 8d 7d d8 e8 d3 9f ff ff 48 85 c0 75 dd 48 8d 7d d8 e8 75 a0 ff ff e9 45 fe ff ff <0f> ff e9 3a ff ff ff 0f ff 48 83 c4 10 5b 41 5c 41 5d 5d c3 66 
[  269.687849] ---[ end trace fe5f521401be8a80 ]---

Full logs: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3051/fi-gdg-551/igt@drv_module_reload@basic-reload.html