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Kernel 6.12 - booting hanged in real PREEMPT_RT mode
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Oleksa75
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PostPosted: Tue Nov 19, 2024 1:53 pm    Post subject: Kernel 6.12 - booting hanged in real PREEMPT_RT mode Reply with quote

Hello there!

As we know, the real big one for release 6.12 is the enabling of PREEMPT_RT, implementing real-time computing capabilities.

Kernel from Gentoo repos was compiled OK, but I am unable to boot with it - the process hanging with strange phrases smth like "group root:root is invalid".

Please, can you help me to build an investigation plan and find the root of the reason?

Thanks!
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CaptainBlood
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PostPosted: Tue Nov 19, 2024 5:19 pm    Post subject: Reply with quote

Been manually maintaining a specific branch of gentoo-sources with rt flavor for about a decade with almost no upgrade issue.

Migrating 6.11.1 .config to 6.12.0 currently fails to boot.
Console is frozen.
More work is needed for better understanding.

Thks 4 ur attention, interest & support.
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Hu
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PostPosted: Tue Nov 19, 2024 5:47 pm    Post subject: Re: Kernel 6.12 - booting hanged in real PREEMPT_RT mode Reply with quote

Oleksa75 wrote:
As we know, the real big one for release 6.12 is the enabling of PREEMPT_RT, implementing real-time computing capabilities.

Kernel from Gentoo repos was compiled OK, but I am unable to boot with it
Are you unable to boot any 6.12 kernel, or only unable to boot a PREEMPT_RT 6.12 kernel (but a non-PREEMPT_RT 6.12 kernel works fine)?
Oleksa75 wrote:
- the process hanging with strange phrases smth like "group root:root is invalid".
That does not seem like a kernel message. Please give us the exact message, and describe in more detail how you built the non-working kernel. What initramfs (if any) does it use?
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CaptainBlood
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PostPosted: Tue Nov 19, 2024 6:10 pm    Post subject: Reply with quote

All non rt 6.12.0 branches boot fine here, graphic stack included.

Thks 4 ur attention, interest & support.
_________________
USE="-* ..." in /etc/portage/make.conf here, i.e. a countermeasure to portage implicit braces, belt & diaper paradigm
LT: "I've been doing a passable imitation of the Fontana di Trevi, except my medium is mucus. Sooo much mucus. "


Last edited by CaptainBlood on Tue Nov 19, 2024 6:54 pm; edited 1 time in total
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CaptainBlood
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PostPosted: Tue Nov 19, 2024 6:44 pm    Post subject: Reply with quote

I rederived a minimal working 6.12.0 .config to rt.
6.12 rt system boots fine, but display-manager fails to start.
Graphic stack seems failing.

Skylake iGP here.



Thks 4 ur attention, interest & support.
_________________
USE="-* ..." in /etc/portage/make.conf here, i.e. a countermeasure to portage implicit braces, belt & diaper paradigm
LT: "I've been doing a passable imitation of the Fontana di Trevi, except my medium is mucus. Sooo much mucus. "
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Oleksa75
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PostPosted: Tue Nov 19, 2024 7:19 pm    Post subject: Reply with quote

CaptainBlood wrote:
I rederived a minimal working 6.12.0 .config to rt.
6.12 rt system boots fine, but display-manager fails to start.
Graphic stack seems failing.

Skylake iGP here.


Thks 4 ur attention, interest & support.


Correct! The same for me, and seems I've found root of reason

Code:
thinkbox /tmp # lspci -nnkv | grep -i VGA


00:02.0 VGA compatible controller [0300]: Intel Corporation Raptor Lake-P [UHD Graphics] [8086:a721] (rev 04) (prog-if 00 [VGA controller])

thinkbox /tmp # make menuconfig

Then select

Device Drivers > Graphics support > Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)

<M> Intel Xe Graphics

In section "Force probe xe for selected Intel hardware IDs" I posted "a721"

This force procedure leads to unable boot with real RT:

[1.341040] xe 0000:00:02.0: Your graphics device a721 is not officially supported
by xe driver in this kernel version. To force Xe probe,
use xe.force_probe='a721' and i915.force_probe='!a721'
module parameters or CONFIG_DRM_XE_FORCE_PROBE='a721' and
CONFIG_DRM_I915_FORCE_PROBE='!a721' configuration options.
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CaptainBlood
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PostPosted: Tue Nov 19, 2024 8:16 pm    Post subject: Reply with quote

Here
Code:
Symbol: DRM_I915_FORCE_PROBE [=]
  │ Type  : string
  │ Defined at drivers/gpu/drm/i915/Kconfig:58
  │   Prompt: Force probe i915 for selected Intel hardware IDs
  │   Depends on: HAS_IOMEM [=y] && DRM [=y] && DRM_I915 [=n]
  │   Location:
  │     -> Device Drivers
  │       -> Graphics support
  │ (1)     -> Direct Rendering Manager (XFree86 4.1.0 and higher DRI support) (DRM [=y])
  │           -> Intel 8xx/9xx/G3x/G4x/HD Graphics (DRM_I915 [=n])
  │             -> Force probe i915 for selected Intel hardware IDs (DRM_I915_FORCE_PROBE [=])
Code:
Symbol: DRM_I915 [=n]                                                                       
  │ Type  : tristate
  │ Defined at drivers/gpu/drm/i915/Kconfig:2
  │   Prompt: Intel 8xx/9xx/G3x/G4x/HD Graphics
  │   Depends on: HAS_IOMEM [=y] && DRM [=y] && X86 [=y] && PCI [=y] && !PREEMPT_RT [=y]
  │   Location:
  │     -> Device Drivers
  │       -> Graphics support
  │ (1)     -> Direct Rendering Manager (XFree86 4.1.0 and higher DRI support) (DRM [=y])
  │           -> Intel 8xx/9xx/G3x/G4x/HD Graphics (DRM_I915 [=n])
Plz note !PREEMPT_RT.

So path to such a clue seems unaccessible on Skylake iGP.

Thks 4 ur attention, interest & support.
_________________
USE="-* ..." in /etc/portage/make.conf here, i.e. a countermeasure to portage implicit braces, belt & diaper paradigm
LT: "I've been doing a passable imitation of the Fontana di Trevi, except my medium is mucus. Sooo much mucus. "
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