| Summary: | N450 and D510 machines get stuck in igt@gem_ringfill@basic-default-hang | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Product: | DRI | Reporter: | Tomi Sarvela <tomi.p.sarvela> | ||||||||||||||||||||||
| Component: | DRM/Intel | Assignee: | Chris Wilson <chris> | ||||||||||||||||||||||
| Status: | CLOSED FIXED | QA Contact: | Intel GFX Bugs mailing list <intel-gfx-bugs> | ||||||||||||||||||||||
| Severity: | critical | ||||||||||||||||||||||||
| Priority: | high | CC: | bugs, conselvan2, humberto.i.perez.rodriguez, intel-gfx-bugs, jani.saarinen, luis.botello.ortega, marta.lofstedt, ramix.ben.hassine | ||||||||||||||||||||||
| Version: | DRI git | Keywords: | bisected, regression | ||||||||||||||||||||||
| Hardware: | x86-64 (AMD64) | ||||||||||||||||||||||||
| OS: | Linux (All) | ||||||||||||||||||||||||
| Whiteboard: | ReadyForDev | ||||||||||||||||||||||||
| i915 platform: | G33, PNV | i915 features: | display/Other | ||||||||||||||||||||||
| Attachments: |
|
||||||||||||||||||||||||
And the actual cause for this regression are the direct i915_reset() calls added by:
4680816be336 ("drm/i915: Wait first for submission, before waiting for request completion")
221fe7994554 ("drm/i915: Perform a direct reset of the GPU from the waiter")
As the GPU reset kills the display engine on these old platforms, you can't just go yanking on the reset line at any time. The procedure used by i915_reset_and_wakeup() is to disable all display functions first, then perform the reset, and finally re-enable the display functions. That is safe, whereas anything else isn't really.
The spec (the old configdb which no longer exists sadly) suggested that one should at least disable all planes before yanking on the reset, but as is demonstrated by this failure mode even that isn't sufficient. If you yank the reset at the wrong time you could even hard hang the machine (eg. by poking at the LUT with the DPLL off).
1. Stop taking struct_mutex when disabling crtcs and installing no framebuffers [eek intel_overlay_disable] 2. Do intel_prepare_reset before reset handoff 3. Do intel_finish_reset as normal *** Bug 99894 has been marked as a duplicate of this bug. *** *** Bug 99903 has been marked as a duplicate of this bug. *** Failure rate 1/60 run(s) (1%) No changes in the past 10 days. Raising the priority to get inputs from developers. Still popping out every now and then - Failure rate 2/221 run(s) igt@gem_ringfill@basic-default-hang - fi-pnv-d510 - incomplete - 2017-04-10 igt@gem_ringfill@basic-default-hang - fi-pnv-d510 - incomplete - 2017-03-13 PNV-D510 is not part of the regular farm. I'm running CI_DRM manually every now and then to remind that this bug exists. Note: reproduction rate is stable 100% Adding tag into "Whiteboard" field - ReadyForDev The bug still active *Status is correct *Platform is included *Feature is included *Priority and Severity correctly set *Logs included *** Bug 100985 has been marked as a duplicate of this bug. *** This also affects BLK and ELK. *** Bug 101063 has been marked as a duplicate of this bug. *** *** Bug 101077 has been marked as a duplicate of this bug. *** This is blocking many new (SKL+) platforms, raising priority. We need some progress on this now. Adding i915 platforms due to *** Bug 101077 has been marked as a duplicate of this bug. *** *** Bug 101231 has been marked as a duplicate of this bug. *** Tested all kms_busy with Chris patch on BDW NUCi5: https://patchwork.freedesktop.org/patch/162894/ drm-tip: 43495097d5a36910d157019be4d47696d6fabeab drm/i915: Break modeset deadlocks on reset 7f2c92652872fbbe37c8bca92eccb7218100c21d drm-tip: 2017y-06m-22d-08h-47m-32s UTC integration manifest I either still hang on 3rdf subtest: extended-pageflip-modeset-hang-oldfb-default-A or I fail at some of the early kms_busy@extended-pageflip_* subtests followed by all remaining kms_busy subtestes are skipped. add dmesg for both cases. Maybe Bug 101231 isn't duplicate after all. Created attachment 132137 [details]
dmesg chris patch skipped tests
Created attachment 132138 [details]
efi pstore dmesg chris patch machine hung
(In reply to Marta Löfstedt from comment #17) > I either still hang on 3rdf subtest: > extended-pageflip-modeset-hang-oldfb-default-A extended-pageflip-modeset-hang-* exhibit multiple bugs, once of which is a deadlock prevented (not fixed!) by the wedging. However, prior to hitting the deadlock you encounter many use-after-frees in the atomic modesetting. FYI issue reproduced with the v3: https://patchwork.freedesktop.org/patch/163147/ But, if Chris patch fixes the old machines from hanging on CI. We could un-duplicate Bug 101231 and continue working with the kms_busy@extendes-* issue in that one. The following tests PASS on BSW with this configuration
Tests List:
igt@gem_ringfill@basic-default-hang
This is my configuration:
**************************************************************
* * * * * * * * HARDWARE SPECIFICATIONS * * * * * * * * * * *
**************************************************************
==============================================================
Essentials
==============================================================
Processor Number N3700
Status Launched
Launch Date Q1'15
Lithography 14 nm
==============================================================
Performance
==============================================================
# of Cores 4
# of Threads 4
Processor Base Frequency 1.60 GHz
Burst Frequency 2.40 GHz
Cache 2 MB L2
TDP 6 W
Scenario Design Power (SDP) 4 W
==============================================================
Memory Specifications
==============================================================
Max Memory Size 8 GB
Memory Types DDR3L-1600
Max # of Memory Channels 2
ECC Memory Supported No
==============================================================
Graphics Specifications
==============================================================
Processor Graphics Intel® HD Graphics
Graphics Base Frequency 400.00 MHz
Graphics Burst Frequency 700.00 MHz
Graphics Video Max Memory 8 GB
Graphics Output eDP/DP/HDMI
Execution Units 16
DirectX* Support Yes
OpenGL* Support Yes
Intel® Quick Sync Video Yes
Intel® InTru™ 3D Technology No
Intel® Clear Video HD Technology Yes
Intel® Clear Video Technology Yes
Intel® Wireless Display Yes
# of Displays Supported 3
====================================================
Graphic Stack
====================================================
Component: drm
tag: libdrm-2.4.81-33-g3876bc2
commit: 3876bc246a07070a6043159cd7623d4def9bbd4c
Component: cairo
tag: 1.15.6-2-g57b4050
commit: 57b40507dda3f58dfc8635548d606b86dc7bcf51
Component: intel-gpu-tools
tag: intel-gpu-tools-1.19-112-g493151b
commit: 493151b0768aa4ca535cef49cb7efa174a9c3a77
Component: piglit
tag: piglit-v1
commit: 973892687cf5c2f8e2dbe1d22998b82736643787
The following tests PASS on BDW with this configuration
Tests List:
igt@gem_ringfill@basic-default-hang
This is my configuration:
**************************************************************
* * * * * * * * HARDWARE SPECIFICATIONS * * * * * * * * * * *
**************************************************************
====================================================
Graphic Stack
====================================================
Component: drm
tag: libdrm-2.4.81-42-g4d24415
commit: 4d244155945f5531b4d9735bbe73c887aac81070
Component: cairo
tag: 1.15.6-13-g495cb9a
commit: 495cb9a0a765ccbc678f55d8bfe699829a214f39
Component: intel-gpu-tools
tag: intel-gpu-tools-1.19-166-geeff6a1
commit: eeff6a1d9c4e2c195b30ad95ee36a58ef6ca3387
Component: piglit
tag: piglit-v1
commit: 23ed442ed690e1b61e372703375f27375025dee6
======================================
Software
======================================
kernel version : 4.13.0-rc4-drm-tip-ww32-commit-3d87f89+
hostname : BDW-2-NUC5i7RYB
architecture : x86_64
os version : Ubuntu 16.10
os codename : yakkety
kernel driver : i915
bios revision : 5.6
bios release date : 05/29/2015
hardware acceleration : [91mdisabled[0m
swap partition : [92menabled[0m on (/dev/sda3)
======================================
Graphic drivers
======================================
grep: /opt/X11R7/var/log/Xorg.0.log: No such file or directory
libdrm : 2.4.82
cairo : 1.15.7
intel-gpu-tools (tag) : intel-gpu-tools-1.19-166-geeff6a1
intel-gpu-tools (commit) : eeff6a1
======================================
Hardware
======================================
platform : Broadwell
motherboard id : NUC5i7RYB
form factor : Desktop
cpu family : Core i7
cpu family id : 6
cpu information : Intel(R) Core(TM) i7-5557U CPU @ 3.10GHz
gpu card : Intel Corporation Iris Graphics 6100 (rev 09) (prog-if 00 [VGA controller])
memory ram : 7.71 GB
max memory ram : 16 GB
cpu thread : 4
cpu core : 2
cpu model : 61
cpu stepping : 4
socket : Socket BGA1168
signature : Type 0, Family 6, Model 61, Stepping 4
hard drive : 447GiB (480GB)
current cd clock frequency : 337500 kHz
maximum cd clock frequency : 540000 kHz
displays connected : HDMI-A-1 DP-1
======================================
Firmware
======================================
======================================
kernel parameters
======================================
quiet drm.debug=0x1e resume=/dev/sda3 fastboot
Note: Removing BDW from this BUG since test is shown as PASSED...
Created attachment 133386 [details]
Tests Log (BDW)
Created attachment 133387 [details]
Dmesg.log (BDW)
The following tests PASS on BSW with this configuration
Tests List:
igt@gem_ringfill@basic-default-hang
This is my configuration:
**************************************************************
* * * * * * * * HARDWARE SPECIFICATIONS * * * * * * * * * * *
**************************************************************
======================================
Software
======================================
kernel version : 4.13.0-rc4-drm-tip-ww32-commit-3d87f89+
hostname : BSW-2-BRASWELL
architecture : x86_64
os version : Ubuntu 16.10
os codename : yakkety
kernel driver : i915
bios revision : 0.33
bios release date : 08/12/2015
ksc : 0.16
hardware acceleration : disabled
swap partition : enabled on (/dev/sda3)
======================================
Graphic drivers
======================================
grep: /opt/X11R7/var/log/Xorg.0.log: No such file or directory
libdrm : 2.4.82
cairo : 1.15.7
intel-gpu-tools (tag) : intel-gpu-tools-1.19-166-geeff6a1
intel-gpu-tools (commit) : eeff6a1
======================================
Hardware
======================================
platform : Braswell
motherboard model : 10G9000NUS
motherboard id : BRASWELL
form factor : Desktop
manufacturer : LENOVO
cpu family : Pentium
cpu family id : 6
cpu information : Intel(R) Pentium(R) CPU N3700 @ 1.60GHz
gpu card : Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Integrated Graphics Controller (rev 21) (prog-if 00 [VGA controller])
memory ram : 7.68 GB
max memory ram : 8 GB
cpu thread : 4
cpu core : 4
cpu model : 76
cpu stepping : 3
socket : Socket BGA1155
signature : Type 0, Family 6, Model 76, Stepping 3
hard drive : 476GiB (512GB)
current cd clock frequency : 266667 kHz
maximum cd clock frequency : 320000 kHz
displays connected : DP-1 DP-3
======================================
Firmware
======================================
======================================
kernel parameters
======================================
quiet drm.debug=0x1e resume=/dev/sda3 fastboot
Note: Removing BSW from this BUG since test is shown as PASSED...
Created attachment 133388 [details]
Tests Log (BSW)
Created attachment 133389 [details]
Dmesg.log (BSW)
This is the Graphic Stack of comment 26 (BSW) Component: drm tag: libdrm-2.4.81-42-g4d24415 commit: 4d244155945f5531b4d9735bbe73c887aac81070 Component: cairo tag: 1.15.6-13-g495cb9a commit: 495cb9a0a765ccbc678f55d8bfe699829a214f39 Component: intel-gpu-tools tag: intel-gpu-tools-1.19-166-geeff6a1 commit: eeff6a1d9c4e2c195b30ad95ee36a58ef6ca3387 Component: piglit tag: piglit-v1 commit: 23ed442ed690e1b61e372703375f27375025dee6 The following tests Fail on BXT with this configuration
Tests List:
igt@gem_ringfill@basic-default-hang
This is my configuration:
**************************************************************
* * * * * * * * HARDWARE SPECIFICATIONS * * * * * * * * * * *
**************************************************************
Component: drm
tag: libdrm-2.4.81-42-g4d24415
commit: 4d244155945f5531b4d9735bbe73c887aac81070
Component: cairo
tag: 1.15.6-13-g495cb9a
commit: 495cb9a0a765ccbc678f55d8bfe699829a214f39
Component: intel-gpu-tools
tag: intel-gpu-tools-1.19-166-geeff6a1
commit: eeff6a1d9c4e2c195b30ad95ee36a58ef6ca3387
Component: piglit
tag: piglit-v1
commit: 23ed442ed690e1b61e372703375f27375025dee6
======================================
Software
======================================
kernel version : 4.13.0-rc4-drm-tip-ww32-commit-3d87f89+
hostname : BXT-1
architecture : x86_64
os version : Ubuntu 16.10
os codename : yakkety
kernel driver : i915
bios revision : 5.6
bios release date : 06/19/2017
ksc : 18.0
hardware acceleration : disabled
swap partition : enabled on (/dev/sda3)
======================================
Graphic drivers
======================================
grep: /opt/X11R7/var/log/Xorg.0.log: No such file or directory
libdrm : 2.4.82
cairo : 1.15.7
intel-gpu-tools (tag) : intel-gpu-tools-1.19-166-geeff6a1
intel-gpu-tools (commit) : eeff6a1
======================================
Hardware
======================================
motherboard model : NUC6CAYS
motherboard id : NUC6CAYB
form factor : Desktop
manufacturer : Intelcorporation
cpu family : Celeron
cpu family id : 6
cpu information : Intel(R) Celeron(R) CPU J3455 @ 1.50GHz
gpu card : Intel Corporation Device 5a85 (rev 0b) (prog-if 00 [VGA controller])
memory ram : 15.54 GB
max memory ram : 32 GB
cpu thread : 4
cpu core : 4
cpu model : 92
cpu stepping : 9
socket : Other
signature : Type 0, Family 6, Model 92, Stepping 9
hard drive : 74GiB (80GB)
current cd clock frequency : 384000 kHz
maximum cd clock frequency : 624000 kHz
displays connected : DP-1 DP-2
======================================
Firmware
======================================
dmc fw loaded : yes
dmc version : 1.7
guc fw loaded : SUCCESS
guc version wanted : 8.7
guc version found : 8.7
huc fw loaded : yes
======================================
kernel parameters
======================================
quiet drm.debug=0x1e i915.enable_guc_loading=2 i915.enable_guc_submission=2 auto panic=1 nmi_watchdog=panic resume=/dev/sda3 fastboot
Note: The platform fully hang during the test, so no test log was generated, instead i added a dmesg log...(dmesg -w)...
Created attachment 133390 [details]
Dmesg.log (BXT)
The following tests Fail on SKL with this configuration
Tests List:
igt@gem_ringfill@basic-default-hang
This is my configuration:
**************************************************************
* * * * * * * * HARDWARE SPECIFICATIONS * * * * * * * * * * *
**************************************************************
Component: drm
tag: libdrm-2.4.81-42-g4d24415
commit: 4d244155945f5531b4d9735bbe73c887aac81070
Component: cairo
tag: 1.15.6-13-g495cb9a
commit: 495cb9a0a765ccbc678f55d8bfe699829a214f39
Component: intel-gpu-tools
tag: intel-gpu-tools-1.19-166-geeff6a1
commit: eeff6a1d9c4e2c195b30ad95ee36a58ef6ca3387
Component: piglit
tag: piglit-v1
commit: 23ed442ed690e1b61e372703375f27375025dee6
======================================
Software
======================================
kernel version : 4.13.0-rc4-drm-tip-ww32-commit-3d87f89+
hostname : SKL-2-NUC6i5SYB
architecture : x86_64
os version : Ubuntu 16.10
os codename : yakkety
kernel driver : i915
bios revision : 5.6
bios release date : 05/27/2016
hardware acceleration : disabled
swap partition : enabled on (/dev/sda3)
======================================
Graphic drivers
======================================
grep: /opt/X11R7/var/log/Xorg.0.log: No such file or directory
libdrm : 2.4.82
cairo : 1.15.7
intel-gpu-tools (tag) : intel-gpu-tools-1.19-166-geeff6a1
intel-gpu-tools (commit) : eeff6a1
======================================
Hardware
======================================
platform : Skylake-Nuc
motherboard id : NUC6i5SYB
form factor : Desktop
cpu family : Core i5
cpu family id : 6
cpu information : Intel(R) Core(TM) i5-6260U CPU @ 1.80GHz
gpu card : Intel Corporation Iris Graphics 540 (rev 0a) (prog-if 00 [VGA controller])
memory ram : 15.58 GB
max memory ram : 32 GB
cpu thread : 4
cpu core : 2
cpu model : 78
cpu stepping : 3
socket : None
signature : Type 0, Family 6, Model 78, Stepping 3
hard drive : 223GiB (240GB)
current cd clock frequency : 337500 kHz
maximum cd clock frequency : 675000 kHz
displays connected : HDMI-A-1 DP-1
======================================
Firmware
======================================
dmc fw loaded : yes
dmc version : 1.26
guc fw loaded : SUCCESS
guc version wanted : 6.1
guc version found : 6.1
huc fw loaded : yes
======================================
kernel parameters
======================================
quiet drm.debug=0x1e i915.enable_guc_loading=2 i915.enable_guc_submission=2 auto panic=1 nmi_watchdog=panic resume=/dev/sda3 fastboot
Note: The platform hang during the test, so no test log was generated, instead i added a dmesg log...(dmesg -w)...
Created attachment 133391 [details]
Dmesg.log (SKL)
The following tests Fail on KBL with this configuration
Tests List:
igt@gem_ringfill@basic-default-hang
This is my configuration:
**************************************************************
* * * * * * * * HARDWARE SPECIFICATIONS * * * * * * * * * * *
**************************************************************
Component: drm
tag: libdrm-2.4.81-42-g4d24415
commit: 4d244155945f5531b4d9735bbe73c887aac81070
Component: cairo
tag: 1.15.6-13-g495cb9a
commit: 495cb9a0a765ccbc678f55d8bfe699829a214f39
Component: intel-gpu-tools
tag: intel-gpu-tools-1.19-166-geeff6a1
commit: eeff6a1d9c4e2c195b30ad95ee36a58ef6ca3387
Component: piglit
tag: piglit-v1
commit: 23ed442ed690e1b61e372703375f27375025dee6
======================================
Software
======================================
kernel version : 4.13.0-rc4-drm-tip-ww32-commit-3d87f89+
hostname : KBL-2
architecture : x86_64
os version : Ubuntu 16.10
os codename : yakkety
kernel driver : i915
bios revision : 5.6
bios release date : 05/03/2017
ksc : 8.1
hardware acceleration : disabled
swap partition : enabled on (/dev/sda3)
======================================
Graphic drivers
======================================
grep: /opt/X11R7/var/log/Xorg.0.log: No such file or directory
libdrm : 2.4.82
cairo : 1.15.7
intel-gpu-tools (tag) : intel-gpu-tools-1.19-166-geeff6a1
intel-gpu-tools (commit) : eeff6a1
======================================
Hardware
======================================
motherboard id : NUC7i5BNB
form factor : Desktop
cpu family : Core i5
cpu family id : 6
cpu information : Intel(R) Core(TM) i5-7260U CPU @ 2.20GHz
gpu card : Intel Corporation Device 5926 (rev 06) (prog-if 00 [VGA controller])
memory ram : 15.58 GB
max memory ram : 32 GB
cpu thread : 4
cpu core : 2
cpu model : 142
cpu stepping : 9
socket : Other
signature : Type 0, Family 6, Model 142, Stepping 9
hard drive : 447GiB (480GB)
current cd clock frequency : 337500 kHz
maximum cd clock frequency : 675000 kHz
displays connected : DP-1 DP-2
======================================
Firmware
======================================
dmc fw loaded : yes
dmc version : 1.1
guc fw loaded : SUCCESS
guc version wanted : 9.14
guc version found : 9.14
huc fw loaded : yes
======================================
kernel parameters
======================================
quiet drm.debug=0x1e i915.enable_guc_loading=2 i915.enable_guc_submission=2 auto panic=1 nmi_watchdog=panic resume=/dev/sda3 fastboot
Note: The platform hang during the test, so no test log was generated, instead i added a dmesg log...(dmesg -w)...
Created attachment 133392 [details]
Dmesg.log (KBL)
The following tests Fail on GLK with this configuration
Tests List:
igt@gem_ringfill@basic-default-hang
This is my configuration:
**************************************************************
* * * * * * * * HARDWARE SPECIFICATIONS * * * * * * * * * * *
**************************************************************
Component: drm
tag: libdrm-2.4.81-42-g4d24415
commit: 4d244155945f5531b4d9735bbe73c887aac81070
Component: cairo
tag: 1.15.6-13-g495cb9a
commit: 495cb9a0a765ccbc678f55d8bfe699829a214f39
Component: intel-gpu-tools
tag: intel-gpu-tools-1.19-166-geeff6a1
commit: eeff6a1d9c4e2c195b30ad95ee36a58ef6ca3387
Component: piglit
tag: piglit-v1
commit: 23ed442ed690e1b61e372703375f27375025dee6
======================================
Software
======================================
kernel version : 4.13.0-rc4-drm-tip-ww32-commit-3d87f89+
hostname : GLK-2-GLKRVP1DDR405
architecture : x86_64
os version : Ubuntu 16.10
os codename : yakkety
kernel driver : i915
bios revision : 50.51
bios release date : 06/02/2017
ksc : 1.32
hardware acceleration : disabled
swap partition : enabled on (/dev/sda3)
======================================
Graphic drivers
======================================
grep: /opt/X11R7/var/log/Xorg.0.log: No such file or directory
libdrm : 2.4.82
cairo : 1.15.7
intel-gpu-tools (tag) : intel-gpu-tools-1.19-166-geeff6a1
intel-gpu-tools (commit) : eeff6a1
======================================
Hardware
======================================
platform : Geminilake
motherboard model : Geminilake
motherboard id : GLKRVP1DDR4(05)
form factor : Hand Held
manufacturer : IntelCorp.
cpu family : Other
cpu family id : 6
cpu information : Genuine Intel(R) CPU @ 1.10GHz
gpu card : Intel Corporation Device 3184 (rev 01) (prog-if 00 [VGA controller])
memory ram : 3.67 GB
max memory ram : 16 GB
cpu thread : 4
cpu core : 4
cpu model : 122
cpu stepping : 0
socket : Other
hard drive : 74GiB (80GB)
current cd clock frequency : 79200 kHz
maximum cd clock frequency : 316800 kHz
displays connected : eDP-1 DP-1 HDMI-A-2
======================================
Firmware
======================================
dmc fw loaded : yes
dmc version : 1.4
guc fw loaded : SUCCESS
guc version wanted : 10.56
guc version found : 10.56
huc fw loaded : yes
======================================
kernel parameters
======================================
quiet drm.debug=0x1e i915.enable_guc_loading=2 i915.enable_guc_submission=2 i915.alpha_support=1 auto panic=1 nmi_watchdog=panic resume=/dev/sda3 fastboot
Note: The platform hang during the test, so no test log was generated, instead i added a dmesg log...(dmesg -w)...
Created attachment 133393 [details]
Dmesg.log (GLK)
This issues is not presenting in GLK, BXT, SKL or KBL removing from platforms affected. but continues to fail in PNV will remain open Removing G45 since it don't fail on ELK anymore: https://intel-gfx-ci.01.org/tree/drm-tip/fi-elk-e7500.html This tests continue failing on BLB/PNV CI igt@gem_ringfill@basic-default-hang https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3521/fi-blb-e6850/igt@gem_ringfill@basic-default-hang.html https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_3521/fi-pnv-d510/igt@gem_ringfill@basic-default-hang.html Why are there non-Pineview devices listed here? This bug was for the gen3 specific failure that occurred if we reset the GPU with the display still connected. Closing, please re-open if still occurs. |
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Pineview testshosts I've tested seem to hang forever in following code when tested with igt@gem_ringfill@basic-default-hang. Comment from vsyrjala implied that the GPU hang reset messes PLL when done in wrong time. No dmesg is left behind. This spot was found with gratuitous adding of DRM_DEBUGs. The bug has been around in drm-intel-nightly / drm-tip for at least two months. drivers/gpu/drm/i915/i915_irq.c:i915_get_vblank_counter(): /* * High & low register fields aren't synchronized, so make sure * we get a low value that's stable across two reads of the high * register. */ do { high1 = I915_READ(high_frame) & PIPE_FRAME_HIGH_MASK; low = I915_READ(low_frame); high2 = I915_READ(high_frame) & PIPE_FRAME_HIGH_MASK; } while (high1 != high2);