Happens only on ICL-U, occured so far during the following tests:
- igt@gem_exec_nop@basic-series
- igt@drv_selftest@live_requests
- igt@gem_exec_nop@basic-parallel

<3>[  105.910240] execlists_submit_ports:434 GEM_BUG_ON(count > !n)
<4>[  105.910357] ------------[ cut here ]------------
<2>[  105.910359] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:434!
<4>[  105.910384] invalid opcode: 0000 [#1] PREEMPT SMP PTI
<4>[  105.910393] CPU: 6 PID: 1182 Comm: gem_exec_nop Tainted: G     U  W         4.19.0-rc8-CI-Patchwork_10556+ #1
<4>[  105.910404] Hardware name: Intel Corporation Ice Lake Client Platform/IceLake U DDR4 SODIMM PD RVP, BIOS ICLSFWR1.R00.2392.A04.1809260455 09/26/2018
<4>[  105.910463] RIP: 0010:__execlists_submission_tasklet+0xa72/0xc20 [i915]
<4>[  105.910473] Code: dd 09 f0 e0 48 8b 35 c5 ed 19 00 49 c7 c0 d8 0b 2e a0 b9 b2 01 00 00 48 c7 c2 50 6b 2c a0 48 c7 c7 6d 96 1f a0 e8 ae 99 f6 e0 <0f> 0b 48 c7 c1 f0 ec 2f a0 ba f3 01 00 00 48 c7 c6 90 6b 2c a0 48
<4>[  105.910492] RSP: 0018:ffffc90000a83948 EFLAGS: 00010086
<4>[  105.910500] RAX: 000000000000000a RBX: ffff8804a887a5d0 RCX: 0000000000000000
<4>[  105.910509] RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff8804ae251fe8
<4>[  105.910518] RBP: ffffc90000a839a8 R08: 0000000000095613 R09: ffff8804ad8f7000
<4>[  105.910526] R10: 0000000000000000 R11: ffff8804ae251fe8 R12: ffff8804a2036340
<4>[  105.910535] R13: 0000000000000000 R14: ffff8804a887a5d0 R15: ffff8804a887a158
<4>[  105.910544] FS:  00007f54e092b980(0000) GS:ffff8804aff80000(0000) knlGS:0000000000000000
<4>[  105.910553] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4>[  105.910561] CR2: 00005645fb626920 CR3: 000000049c9f6001 CR4: 0000000000760ee0
<4>[  105.910570] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
<4>[  105.910579] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
<4>[  105.910587] PKRU: 55555554
<4>[  105.910595] Call Trace:
<4>[  105.910642]  execlists_submit_request+0x181/0x190 [i915]
<4>[  105.910682]  submit_notify+0x8d/0x124 [i915]
<4>[  105.910713]  __i915_sw_fence_complete+0x81/0x250 [i915]
<4>[  105.910751]  i915_request_add+0x36b/0x7e0 [i915]
<4>[  105.910787]  i915_gem_do_execbuffer+0x929/0x1590 [i915]
<4>[  105.910797]  ? deactivate_slab.isra.26+0x7a4/0x7e0
<4>[  105.910812]  ? ___slab_alloc.constprop.34+0x221/0x390
<4>[  105.910820]  ? ___slab_alloc.constprop.34+0x221/0x390
<4>[  105.910853]  ? i915_gem_execbuffer2_ioctl+0xc4/0x3f0 [i915]
<4>[  105.910864]  ? lock_acquire+0xa6/0x1c0
<4>[  105.910897]  ? i915_gem_execbuffer_ioctl+0x300/0x300 [i915]
<4>[  105.910930]  i915_gem_execbuffer2_ioctl+0x21b/0x3f0 [i915]
<4>[  105.910963]  ? i915_gem_execbuffer_ioctl+0x300/0x300 [i915]
<4>[  105.910973]  drm_ioctl_kernel+0x81/0xf0
<4>[  105.910981]  drm_ioctl+0x2e6/0x3a0
<4>[  105.911012]  ? i915_gem_execbuffer_ioctl+0x300/0x300 [i915]
<4>[  105.911022]  ? trace_hardirqs_on_thunk+0x1a/0x1c
<4>[  105.911029]  ? lockdep_hardirqs_on+0xe0/0x1b0
<4>[  105.911036]  ? trace_hardirqs_on_thunk+0x1a/0x1c
<4>[  105.911045]  do_vfs_ioctl+0xa0/0x6d0
<4>[  105.911053]  ? retint_kernel+0x2d/0x2d
<4>[  105.911061]  ksys_ioctl+0x35/0x60
<4>[  105.911068]  __x64_sys_ioctl+0x11/0x20
<4>[  105.911074]  do_syscall_64+0x55/0x190
<4>[  105.911081]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4>[  105.911088] RIP: 0033:0x7f54dfbb85d7
<4>[  105.911094] Code: b3 66 90 48 8b 05 b1 48 2d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 81 48 2d 00 f7 d8 64 89 01 48

https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_10758/fi-icl-u/igt@gem_exec_nop@basic-parallel.html
https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_10556/fi-icl-u/igt@gem_exec_nop@basic-series.html
https://intel-gfx-ci.01.org/tree/drm-tip/IGT_4696/fi-icl-u/igt@drv_selftest@live_requests.html
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_3187/fi-icl-u/igt@gem_exec_nop@basic-parallel.html
https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_10569/fi-icl-u/igt@gem_exec_nop@basic-series.html
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_3185/fi-icl-u/igt@drv_selftest@live_requests.html
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_5089/fi-icl-u/dmesg0.log
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_3148/fi-icl-u/igt@drv_selftest@live_requests.html
https://intel-gfx-ci.01.org/tree/drm-tip/IGT_4701/fi-icl-u/igt@drv_selftest@live_requests.html