linux-kernel - Re: [tip:sched/core] [sched/fair] 79104becf4: BUG:kernel_NULL_pointer

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Message-ID: <e9f705f3-3a8f-4952-b5d5-e36f4fa1515d@intel.com>
Date: Tue, 28 Oct 2025 10:30:08 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: kernel test robot <oliver.sang@...el.com>, Fernand Sieber
	<sieberf@...zon.com>, <oe-lkp@...ts.linux.dev>, <lkp@...el.com>,
	<linux-kernel@...r.kernel.org>, <x86@...nel.org>, <aubrey.li@...ux.intel.com>
Subject: Re: [tip:sched/core] [sched/fair] 79104becf4:
 BUG:kernel_NULL_pointer_dereference,address

On 10/27/2025 10:09 PM, Peter Zijlstra wrote:
> On Mon, Oct 27, 2025 at 03:07:18PM +0100, Peter Zijlstra wrote:
>> On Mon, Oct 27, 2025 at 02:55:16PM +0100, Peter Zijlstra wrote:
>>
>>>> May I know if you are using the kernel config 0day attached?
>>>> I found that the config 0day attached
>>>> (https://download.01.org/0day-ci/archive/20251021/202510211205.1e0f5223-lkp@intel.com/config-6.18.0-rc1-00001-g79104becf42b)
>>>> has
>>>> CONFIG_IA32_EMULATION=y
>>>> CONFIG_IA32_EMULATION_DEFAULT_DISABLED=y
>>
>> Yep, deleting that entry makes it all work.
> 
> 'work' might be over stating, it boots and starts trinity, which then
> promptly (as in a handful of seconds) triggers OOM and dies. Not
> actually reproducing the NULL deref I was looking for.

Change the following line in job-script
export memory='16G'
to
export memory='64G'
?

I had a try and can reproduce the NULL except at first run:

[  137.151416][  T321] BUG: kernel NULL pointer dereference, address: 
0000000000000051
[  137.152128][  T321] #PF: supervisor read access in kernel mode
[  137.152661][  T321] #PF: error_code(0x0000) - not-present page
[  137.153155][  T321] PGD 100b76067 P4D 100b76067 PUD 115fd6067 PMD 0
[  137.153834][  T321] Oops: Oops: 0000 [#1]
[  137.154256][  T321] CPU: 0 UID: 65534 PID: 321 Comm: trinity-c1 Not 
tainted 6.18.0-rc1-g30682ad76ee6 #4 PREEMPT
[  137.155384][  T321] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + 
PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[  137.156509][  T321] RIP: 0010:pick_task_fair+0x69/0x9d


thanks,
Chenyu