Re: [BUG] sched/cache: "Make LLC id continuous" causes NULL cpumask dereference in build_sched_domains on POWER9

[Shrikanth Hegde <sshegde@linux.ibm.com>]

On 5/26/26 10:54 AM, Venkat Rao Bagalkote wrote:
> 
> On 26/05/26 9:38 am, Chen, Yu C wrote:
>> Hi Venkat,
>>
>> On 5/26/2026 11:14 AM, Srikar Dronamraju wrote:
>>> * Chen, Yu C <yu.c.chen@intel.com> [2026-05-25 23:35:45]:
>>>
>>>> Hi Venkat,
>>>>
>>>> On 5/25/2026 10:07 PM, Venkat Rao Bagalkote wrote:
>>>>> Greetings!!!
>>>>>
>>>>> I am seeing an early boot kernel panic due to NULL pointer dereference
>>>>> on a POWER9 (pSeries) system when testing linux-next (next-20260522).
> 
> 
> This issue is seen on P11 as well.
> 
> [    0.006697] smp: Brought up 1 node, 16 CPUs
> [    0.006702] Big cores detected but using small core scheduling
> [    0.006752] BUG: Kernel NULL pointer dereference on read at 0x00000000
> [    0.006755] Faulting instruction address: 0xc000000020adbb6c
> [    0.006759] Oops: Kernel access of bad area, sig: 7 [#1]
> [    0.006762] LE PAGE_SIZE=4K MMU=Radix  SMP NR_CPUS=8192 NUMA pSeries
> [    0.006767] Modules linked in:
> [    0.006772] CPU: 4 UID: 0 PID: 1 Comm: swapper/4 Not tainted 7.1.0- 
> rc5-next-20260525 #1 PREEMPT(lazy)
> [    0.006777] Hardware name: IBM,9080-HEX Power11 (architected) 
> 0x820200 0xf000007 of:IBM,FW1110.01 (NH1110_069) hv:phyp pSeries
> [    0.006781] NIP:  c000000020adbb6c LR: c0000000202e5a58 CTR: 
> 0000000000000000
> [    0.006784] REGS: c0000000283d7890 TRAP: 0300   Not tainted (7.1.0- 
> rc5-next-20260525)
> [    0.006788] MSR:  8000000002009033 <SF,VEC,EE,ME,IR,DR,RI,LE>  CR: 
> 44002242  XER: 20040003
> [    0.006796] CFAR: c0000000202e5a54 DAR: 0000000000000000 DSISR: 
> 00080000 IRQMASK: 0
> [    0.006796] GPR00: 0000000000000000 c0000000283d7b50 c000000021abf100 
> 0000000000000010
> [    0.006796] GPR04: 0000000000000010 0000000000000030 0000000000000000 
> c000000028365500
> [    0.006796] GPR08: 0000000000000000 c000000022213598 000000003b77d000 
> 0000000000000000
> [    0.006796] GPR12: c00000002005d8f0 c000000000008000 c0000000283cb578 
> c0000000283cb400
> [    0.006796] GPR16: c0000000283c9000 c000000022218b20 c0000000222330e8 
> 00000000ffffffff
> [    0.006796] GPR20: fffffffffffffff6 0000000000000000 c000000022da36e0 
> 0000000000000000
> [    0.006796] GPR24: 0000000000000000 0000000000000000 c0000000283c9178 
> c0000000227b5f00
> [    0.006796] GPR28: c00000002831c1e8 c000000022db5980 0000000000000000 
> 0000000000000000
> [    0.006835] NIP [c000000020adbb6c] _find_first_bit+0xc/0xc0
> [    0.006842] LR [c0000000202e5a58] build_sched_domains+0x7d8/0xb40
> [    0.006847] Call Trace:
> [    0.006849] [c0000000283d7b50] [c0000000202e5408] 
> build_sched_domains+0x188/0xb40 (unreliable)
> [    0.006854] [c0000000283d7c90] [c000000022034380] 
> sched_init_domains+0x118/0x168
> [    0.006860] [c0000000283d7ce0] [c000000022032b14] 
> sched_init_smp+0xa8/0x158
> [    0.006865] [c0000000283d7d30] [c000000022005674] 
> kernel_init_freeable+0x1ac/0x294
> [    0.006870] [c0000000283d7dd0] [c000000020011718] kernel_init+0x2c/0x1c4
> [    0.006874] [c0000000283d7e30] [c00000002000debc] 
> ret_from_kernel_user_thread+0x14/0x1c
> [    0.006878] ---- interrupt: 0 at 0x0
> [    0.006881] Code: eb610038 7fc3f378 eb810040 eba10048 38210060 
> ebc1fff0 ebe1fff8 7c0803a6 4e800020 7c681b78 7c832379 4d820020 
> <e9280000> 38e3ffff 39400000 78e7d7e2
> [    0.006895] ---[ end trace 0000000000000000 ]---
> [    0.006898]
> 
> 
> Regards,
> 
> Venkat.
> 

Venkat,

Was it on P11 on Shared LPAR?