The HW replied with one more context-switch than we submitted. It is most disturbing. gem_concurrent_blit can typically hit this within a few minutes.

Hitting the same assertion on bxt/gem_concurrent_blit, always has a trail of breadcrumbs like:

[   61.964007] bcs0(3): 0+ rq.seqno=2275 [ctx=91], count=1
[   61.964050] bcs0(1): [3/3] status=1
[   61.964096] bcs0(1): 0+ rq.seqno=2276 [ctx=91], count=2
[   61.964180] bcs0(1): [4/4] status=8002
[   61.964189] bcs0(1): - rq.seqno=2276 [ctx=91], status=8002, count=2
[   61.977615] bcs0(1): [5/5] status=18
[   61.977640] bcs0(1): - rq.seqno=2276 [ctx=91], status=18, count=1
[   61.995341] bcs0(2): 0+ rq.seqno=2277 [ctx=9b], count=1
[   61.995427] bcs0(2): 0+ rq.seqno=2278 [ctx=9b], count=2
[   61.995623] bcs0(1): [0/1] status=1
[   61.995786] bcs0(1): [1/1] status=8002
[   61.995802] bcs0(1): - rq.seqno=2278 [ctx=9b], status=8002, count=2
[   62.008366] bcs0(1): [2/2] status=18
[   62.008391] bcs0(1): - rq.seqno=2278 [ctx=9b], status=18, count=1
[   62.020052] bcs0(0): 0+ rq.seqno=2279 [ctx=8c], count=1
[   62.020142] bcs0(0): 0+ rq.seqno=2280 [ctx=8c], count=2
[   62.020207] bcs0(1): [3/4] status=12
[   62.020219] bcs0(1): - rq.seqno=2280 [ctx=8c], status=12, count=2

^ This is the bogus event. 0x12 == COMPLETE | PREEMPTED, but it is following the ACTIVE->IDLE notification, where we always expect the IDLE->ACTIVE (status=1) afterwards (see examples above). Following the bogus 0x12 wakeup, the context-switch notification never "catches up", i.e. we never see the final context-switch of ELEMENT_SWITCH or IDLE. At that point only a reset seems to cure it.

[   62.020228] bcs0(1): [4/4] status=8002
[   62.020235] bcs0(1): - rq.seqno=2280 [ctx=8c], status=8002, count=1
[   62.024699] bcs0(3): 1+ rq.seqno=2281 [ctx=96], count=1
[   62.024724] bcs0(3): 0+ rq.seqno=2280 [ctx=8c], count=2
[   62.024753] bcs0(1): [5/5] status=8002
[   62.024774] bcs0(1): - rq.seqno=2280 [ctx=8c], status=8002, count=2


Now, answers on a postcard what we are meant to do to this prevent heading into this cul-de-sac.

Based on CI data failure rate of 1 / 105 runs (1 %). Dropping priority.

*** Bug 102705 has been marked as a duplicate of this bug. ***

Here we go again:
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3112/fi-bxt-j4205/igt@kms_busy@basic-flip-c.html

*** Bug 103190 has been marked as a duplicate of this bug. ***

*** Bug 103178 has been marked as a duplicate of this bug. ***

Glk? I thought glk followed the cnl pattern (random context id reported) rather than this pattern of impossible lite-restore following complete | idle.

(In reply to Chris Wilson from comment #8)
> Glk? I thought glk followed the cnl pattern (random context id reported)
> rather than this pattern of impossible lite-restore following complete |
> idle.

Nope, see https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_5993/fi-glk-1/dmesg-1507731622_Panic_2.log definitely glk shares the bxt failure.

Also,

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3209/shard-apl5/igt@kms_busy@extended-pageflip-hang-oldfb-render-B.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3209/shard-apl5/dmesg-1507719682_Oops_1.log
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3209/shard-apl5/dmesg-1507719682_Panic_2.log

ALso on:
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3228/shard-apl7/igt@kms_properties@connector-properties-legacy.html

Note there is an issue that when we get multiple pstore logs on one of the shared machines, you have to compare with dmesg to figure out which one that belong to which shard. In this case it is this pstore backtrace that is relevant:
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3228/shard-apl7/dmesg-1507893658_Panic_2.log

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3237/shard-apl2/igt@kms_cursor_legacy@cursorA-vs-flipA-atomic.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3238/shard-apl2/igt@kms_draw_crc@draw-method-xrgb8888-render-xtiled.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3242/shard-apl2/igt@kms_vblank@query-forked.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3242/shard-apl4/igt@kms_universal_plane@cursor-fb-leak-pipe-B.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3248/shard-apl3/igt@kms_flip@flip-vs-modeset-vs-hang.html

reproduced:
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3251/shard-apl1/igt@kms_draw_crc@draw-method-xrgb2101010-mmap-cpu-ytiled.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3252/shard-apl7/igt@kms_draw_crc@draw-method-xrgb8888-mmap-cpu-untiled.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3253/shard-apl4/igt@kms_cursor_legacy@basic-flip-before-cursor-legacy.html

Reproduced on GLK-shards

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3252/shard-glkb2/igt@kms_frontbuffer_tracking@fbc-2p-primscrn-cur-indfb-move.html
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3252/shard-glkb2/dmesg-1508246195_Oops_1.log

Also,

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3254/shard-glkb1/igt@kms_frontbuffer_tracking@psr-1p-offscren-pri-shrfb-draw-render.html

and:

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3254/shard-glkb1/igt@kms_setmode@basic.html

Note both pstore from shard-glkb1 has the same issue.

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3256/shard-glkb3/igt@kms_frontbuffer_tracking@fbcpsr-2p-shrfb-fliptrack.html

GLk-shards again:

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3257/shard-glkb3/igt@kms_frontbuffer_tracking@psr-2p-primscrn-pri-shrfb-draw-mmap-gtt.html

Also, CI_DRM_3266 fi-skl-6260u:

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3266/fi-skl-6260u/igt@kms_cursor_legacy@basic-flip-after-cursor-varying-size.html

<4>[  284.776232] ------------[ cut here ]------------
<2>[  284.776235] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:782!
<4>[  284.776260] invalid opcode: 0000 [#1] PREEMPT SMP
<4>[  284.776268] Modules linked in: vgem snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic i915 x86_pkg_temp_thermal intel_powerclamp snd_hda_intel snd_hda_codec coretemp snd_hwdep crct10dif_pclmul snd_hda_core crc32_pclmul ghash_clmulni_intel snd_pcm e1000e ptp pps_core mei_me mei prime_numbers pinctrl_sunrisepoint pinctrl_intel i2c_hid
<4>[  284.776320] CPU: 2 PID: 0 Comm: swapper/2 Tainted: G     U          4.14.0-rc5-CI-CI_DRM_3266+ #1
<4>[  284.776329] Hardware name:                  /NUC6i5SYB, BIOS SYSKLi35.86A.0057.2017.0119.1758 01/19/2017
<4>[  284.776338] task: ffff8802652f50c0 task.stack: ffffc900000ac000
<4>[  284.776369] RIP: 0010:intel_lrc_irq_handler+0x304/0x8a0 [i915]
<4>[  284.776375] RSP: 0018:ffff88026ed03ec0 EFLAGS: 00010246
<4>[  284.776382] RAX: ffff8802525545f0 RBX: ffff880252554590 RCX: 0000000000000000
<4>[  284.776389] RDX: 0000000000000000 RSI: ffffffff81d0d974 RDI: ffff8802525542a8
<4>[  284.776396] RBP: ffff88026ed03f18 R08: 0000000000000000 R09: 0000000000000001
<4>[  284.776403] R10: 0000000000000000 R11: 0000000000000000 R12: ffff880259990000
<4>[  284.776409] R13: 0000000000000000 R14: ffffffff81d1849f R15: 0000000000000000
<4>[  284.776417] FS:  0000000000000000(0000) GS:ffff88026ed00000(0000) knlGS:0000000000000000
<4>[  284.776425] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4>[  284.776431] CR2: 00007f6cef3eb000 CR3: 0000000003e0f001 CR4: 00000000003606e0
<4>[  284.776438] Call Trace:
<4>[  284.776442]  <IRQ>
<4>[  284.776447]  ? tasklet_hi_action+0x71/0x120
<4>[  284.776454]  ? __this_cpu_preempt_check+0x13/0x20
<4>[  284.776461]  tasklet_hi_action+0x98/0x120
<4>[  284.776467]  __do_softirq+0xc0/0x4ae
<4>[  284.776473]  irq_exit+0xae/0xc0
<4>[  284.776478]  smp_apic_timer_interrupt+0x9e/0x2e0
<4>[  284.776484]  apic_timer_interrupt+0x9a/0xa0
<4>[  284.776489]  </IRQ>
<4>[  284.776493] RIP: 0010:cpuidle_enter_state+0x136/0x370
<4>[  284.776498] RSP: 0018:ffffc900000afe80 EFLAGS: 00000216 ORIG_RAX: ffffffffffffff10
<4>[  284.776507] RAX: ffff8802652f50c0 RBX: 0000000000020f9c RCX: 0000000000000001
<4>[  284.776514] RDX: 0000000000000000 RSI: ffffffff81d0d974 RDI: ffffffff81cc18d6
<4>[  284.776521] RBP: ffffc900000afeb8 R08: 000000000000071d R09: 0000000000000018
<4>[  284.776528] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002
<4>[  284.776536] R13: 0000000000000002 R14: ffff88026ed25430 R15: 000000424df9c186
<4>[  284.776546]  cpuidle_enter+0x17/0x20
<4>[  284.776551]  call_cpuidle+0x23/0x40
<4>[  284.776557]  do_idle+0x192/0x1e0
<4>[  284.776563]  cpu_startup_entry+0x1d/0x20
<4>[  284.776568]  start_secondary+0x11c/0x140
<4>[  284.776574]  secondary_startup_64+0xa5/0xa5
<4>[  284.776581] Code: 4d c8 05 a0 03 00 00 48 03 81 a8 0b 00 00 44 8b 28 44 89 eb 41 c1 ed 08 41 83 e5 07 83 e3 07 45 89 af 84 03 00 00 e9 af fd ff ff <0f> 0b 0f 0b 41 80 bf 68 03 00 00 00 4c 8b 65 c8 74 1e 41 8b b7 
<1>[  284.776664] RIP: intel_lrc_irq_handler+0x304/0x8a0 [i915] RSP: ffff88026ed03ec0
<4>[  284.776673] ---[ end trace 75789ff91a01554d ]---

CI_DRM_3267 fi-skl-6700hq

<14>[  384.567935] [IGT] kms_flip: exiting, ret=0
<4>[  384.570958] ------------[ cut here ]------------
<2>[  384.570961] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:782!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3267/fi-skl-6700hq/igt@kms_flip@basic-flip-vs-wf_vblank.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3268/shard-glkb4/igt@kms_frontbuffer_tracking@psr-1p-offscren-pri-indfb-draw-pwrite.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3268/shard-glkb5/igt@kms_frontbuffer_tracking@fbcpsr-1p-primscrn-indfb-msflip-blt.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3266/shard-glkb4/igt@kms_frontbuffer_tracking@fbc-2p-scndscrn-pri-indfb-draw-blt.html

BAT-machine fi-skl-6700hq hit this while running: igt@kms_pipe_crc_basic@read-crc-pipe-b-frame-sequence:

kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:782!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3269/fi-skl-6700hq/igt@kms_pipe_crc_basic@read-crc-pipe-b-frame-sequence.html

(In reply to Marta Löfstedt from comment #27)
> BAT-machine fi-skl-6700hq hit this while running:
> igt@kms_pipe_crc_basic@read-crc-pipe-b-frame-sequence:
> 
> kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:782!
> 
> https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3269/fi-skl-6700hq/
> igt@kms_pipe_crc_basic@read-crc-pipe-b-frame-sequence.html

That's not connected to this bug. This bug is very specifically about the hw reporting COMPLETED | PREEMPTED, and not about the interrupt being received after we have finished parsing the CSB after parking the engines.

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3271/fi-cnl-y/igt@gem_exec_flush@basic-batch-kernel-default-uc.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3273/shard-glkb4/igt@kms_frontbuffer_tracking@psr-2p-scndscrn-pri-indfb-draw-mmap-wc.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3271/shard-glkb1/igt@kms_frontbuffer_tracking@fbc-2p-scndscrn-indfb-pgflip-blt.html
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3271/shard-glkb1/dmesg-1508538544_Oops_1.log

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3273/shard-glkb3/dmesg-1508602166_Oops_1.log
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3273/shard-glkb3/igt@kms_flip@blocking-wf_vblank.html

The: "kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:782!" once are now handled in bug 103410.

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3274/shard-glkb4/igt@kms_flip@flip-vs-modeset-interruptible.html

<2>[  322.306569] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:879!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3274/shard-glkb3/igt@kms_busy@extended-modeset-hang-oldfb-render-C.html

<2>[ 3379.405906] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:879!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3275/shard-glkb2/igt@kms_atomic@plane_cursor_legacy.html

41.938315] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:879!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3275/shard-apl2/igt@kms_frontbuffer_tracking@fbc-1p-primscrn-cur-indfb-draw-mmap-cpu.html

<2>[ 1325.066224] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:879!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3275/shard-glkb2/igt@gem_exec_create@forked.html

<2>[   41.938315] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:879!

Talking point:

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 6b10a01dd371..f5be85a01f83 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -905,6 +905,8 @@ static void intel_lrc_irq_handler(unsigned long data)
                        /* After the final element, the hw should be idle */
                        GEM_BUG_ON(port_count(port) == 0 &&
                                   !(status & GEN8_CTX_STATUS_ACTIVE_IDLE));
+                       if (status & GEN8_CTX_STATUS_ACTIVE_IDLE)
+                               mdelay(2);
                }
 
                if (head != execlists->csb_head) {

prevents the COMPLETED | PREEMPT occurring after the COMPLETED | ACTIVE_IDLE. (Or just significantly increased the mtbf to mask the issue.)

Raised priority

More complete would be

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index eeb3622803a8..1df66aeca3ba 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -599,7 +599,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
                         * the driver is unable to keep up the supply of new
                         * work).
                         */
-                       if (port_count(&port[1]))
+                       if (port_count(&port[0]))
                                goto unlock;
 
                        /* WaIdleLiteRestore:bdw,skl

Needs a w/a assigned.

Reminds me of

commit 70962fbe5c75e785d250c04db4d01c18b7316c13
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon Jan 23 13:05:56 2017 +0000

    drm/i915: Remove disable_lite_restore_wa
    
    This w/a (WaEnableForceRestoreInCtxtDescForVCS) was only used for
    preproduction hw, which is no longer in use.  Remove the workaround to
    simplify the code.

but that is only mentioned for VCS, whereas we see the PREEMPT | COMPLETED on, at least, bcs.

<2>[  366.551741] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:888!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3279/shard-glkb5/igt@kms_flip_event_leak.html

CI_DRM_3283 fi-bxt-j4205 igt@kms_busy@basic-flip-c

<2>[  364.185707] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:888!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3283/fi-bxt-j4205/igt@kms_busy@basic-flip-c.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3285/shard-glkb1/igt@kms_frontbuffer_tracking@fbc-2p-primscrn-spr-indfb-move.html

<2>[ 1515.047901] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:888!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3283/shard-apl6/igt@kms_color@ctm-0-5-pipe1.html

<2>[   77.455586] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:888!

CI_DRM_3288 shard-glkb1 igt@kms_flip@flip-vs-panning-vs-hang-interruptible

<2>[  261.125313] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3288/shard-glkb1/dmesg-1509061688_Panic_2.log
https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3288/shard-glkb1/igt@kms_flip@flip-vs-panning-vs-hang-interruptible.html

Note new line again!
GEM_BUG_ON(status & GEN8_CTX_STATUS_PREEMPTED);

CI_DRM_3288 shard-glkb1 igt@kms_frontbuffer_tracking@fbc-2p-primscrn-spr-indfb-draw-pwrite

<2>[  904.259553] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3288/shard-glkb1/igt@kms_frontbuffer_tracking@fbc-2p-primscrn-spr-indfb-draw-pwrite.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3292/shard-glkb2/igt@kms_frontbuffer_tracking@fbcpsr-2p-scndscrn-pri-shrfb-draw-mmap-cpu.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3292/shard-glkb3/igt@kms_frontbuffer_tracking@fbc-2p-primscrn-pri-indfb-draw-mmap-cpu.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3293/shard-glkb1/igt@kms_cursor_legacy@short-flip-after-cursor-atomic-transitions.html

<2>[ 4502.680683] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

<2>[ 2776.149999] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3300/shard-glkb4/igt@kms_flip@flip-vs-panning-interruptible.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3300/shard-glkb2/igt@kms_frontbuffer_tracking@fbc-2p-primscrn-cur-indfb-onoff.html

<2>[ 1043.960206] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

CI_DRM_3304 fi-glk-1 igt@pm_backlight@basic-brightness

<2>[  523.218649] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3304/fi-glk-1/igt@pm_backlight@basic-brightness.html

CI_DRM_3302 shard-apl8 igt@kms_rotation_crc@bad-tiling

<2>[  703.522499] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3302/shard-apl8/igt@kms_rotation_crc@bad-tiling.html

CI_DRM_3301 shard-glkb4 igt@kms_busy@extended-modeset-hang-newfb-render-C

<2>[ 3461.438418] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3301/shard-glkb4/igt@kms_busy@extended-modeset-hang-newfb-render-C.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3307/shard-glkb3/igt@kms_flip@wf_vblank-interruptible.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3307/shard-glkb3/dmesg-1509580929_Panic_2.log
kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3311/shard-apl4/igt@kms_busy@extended-modeset-hang-newfb-render-B.html

<2>[   75.821455] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3313/shard-glkb2/igt@gem_exec_schedule@smoketest-blt.html

<2>[ 1099.391030] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3317/shard-glkb3/igt@kms_flip@flip-vs-rmfb-interruptible.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3317/shard-glkb3/dmesg-1509998109_Panic_2.log

kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3318/shard-glkb2/igt@kms_frontbuffer_tracking@fbc-2p-scndscrn-pri-shrfb-draw-mmap-gtt.html

<2>[ 1839.277970] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3318/shard-glkb1/igt@kms_cursor_legacy@cursora-vs-flipa-atomic-transitions.html

<2>[   90.044653] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3319/shard-glkb4/igt@kms_frontbuffer_tracking@fbc-2p-scndscrn-indfb-msflip-blt.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3319/shard-glkb4/dmesg-1510073961_Panic_2.log
<2>[ 3148.546706] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3319/shard-glkb2/igt@kms_frontbuffer_tracking@psr-2p-scndscrn-cur-indfb-draw-pwrite.html

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3319/shard-glkb2/dmesg-1510073893_Oops_1.log
<2>[  704.851043] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:891!

Also,
https://intel-gfx-ci.01.org/tree/drm-tip/IGTPW_479/shard-apl4/igt@kms_flip_event_leak.html

Reference from Chris: https://patchwork.freedesktop.org/series/33965/

another reference: https://patchwork.freedesktop.org/series/34081/

commit ba74cb10c775c839f6e1d0fabd1e772eabd9c43f
Author: Michel Thierry <michel.thierry@intel.com>
Date:   Mon Nov 20 12:34:58 2017 +0000

    drm/i915/execlists: Delay writing to ELSP until HW has processed the previous write
    
    The hardware needs some time to process the information received in the
    ExecList Submission Port, and expects us to not write anything more until
    it has 'acknowledged' this new submission by sending an IDLE_ACTIVE or
    PREEMPTED CSB event.
    
    If we do not follow this, the driver could write new data into the ELSP
    before HW had finishing fetching the previous one, putting us in
    'undefined behaviour' space.
    
    This seems to be the problem causing the spurious PREEMPTED & COMPLETE
    events after a COMPLETE like the one below:
    
    [] vcs0: sw rd pointer = 2, hw wr pointer = 0, current 'head' = 3.
    [] vcs0:  Execlist CSB[0]: 0x00000018 _ 0x00000007
    [] vcs0:  Execlist CSB[1]: 0x00000001 _ 0x00000000
    [] vcs0:  Execlist CSB[2]: 0x00000018 _ 0x00000007  <<< COMPLETE
    [] vcs0:  Execlist CSB[3]: 0x00000012 _ 0x00000007  <<< PREEMPTED & COMPLETE
    [] vcs0:  Execlist CSB[4]: 0x00008002 _ 0x00000006
    [] vcs0:  Execlist CSB[5]: 0x00000014 _ 0x00000006
    
    The ELSP writes that lead to this CSB sequence show that the HW hadn't
    started executing the previous execlist (the one with only ctx 0x6) by the
    time the new one was submitted; this is a bit more clear in the data
    show in the EXECLIST_STATUS register at the time of the ELSP write.
    
    [] vcs0: ELSP[0] = 0x0_0        [execlist1] - status_reg = 0x0_302
    [] vcs0: ELSP[1] = 0x6_fedb2119 [execlist0] - status_reg = 0x0_8302
    
    [] vcs0: ELSP[2] = 0x7_fedaf119 [execlist1] - status_reg = 0x0_8308
    [] vcs0: ELSP[3] = 0x6_fedb2119 [execlist0] - status_reg = 0x7_8308
    
    Note that having to wait for this ack does not disable lite-restores,
    although it may reduce their numbers.
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102035
    Signed-off-by: Michel Thierry <michel.thierry@intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/<20171118003038.7935-1-michel.thierry@intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20171120123458.23242-4-chris@chris-wilson.co.uk
    Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
    Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

The patch was integrated to CI_DRM_3364. Let's close and archive this issue!

*** Bug 102393 has been marked as a duplicate of this bug. ***