Re: [RFC PATCH v3 13/13] sched/fair: Switch nohz.idle_cpus to use sbm

From: kernel test robot

Date: Sun Oct 18 2026 - 21:07:13 EST

Hello,

kernel test robot noticed "kernel_BUG_at_kernel/smpboot.c" on:

commit: d7dd59cf6a0f621f224947f960403a747b0836f0 ("[RFC PATCH v3 13/13] sched/fair: Switch nohz.idle_cpus to use sbm")
url: https://github.com/intel-lab-lkp/linux/commits/K-Prateek-Nayak/lib-sbm-Introduce-helpers-for-architectures-to-configure-LLC-properties/20261001-192837
patch link: https://lore.kernel.org/all/20261001192849.74788-14-kprateek.nayak@xxxxxxx/
patch subject: [RFC PATCH v3 13/13] sched/fair: Switch nohz.idle_cpus to use sbm

in testcase: boot

config: i386-randconfig-1006-20261010
compiler: clang-22
test machine: qemu-system-i386 -enable-kvm -cpu SandyBridge -smp 4 -m 4G

(please refer to attached dmesg/kmsg for entire log/backtrace)

If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <yi1.lai@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-lkp/202610190859.d3459a50-lkp@xxxxxxxxx

[ 2.426107][ T37] ------------[ cut here ]------------
[ 2.430168][ T37] kernel BUG at kernel/smpboot.c:133!
[ 2.433726][ T37] Oops: invalid opcode: 0000 [#1] SMP PTI
[ 2.436546][ T37] CPU: 3 UID: 0 PID: 37 Comm: ksoftirqd/3 Tainted: G T 7.3.0-rc1+ #1 PREEMPTLAZY
[ 2.436546][ T37] Tainted: [T]=RANDSTRUCT
[ 2.436546][ T37] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 2.436546][ T37] EIP: smpboot_thread_fn (smpboot.c:117)
[ 2.436546][ T37] Code: 83 7e 04 00 74 13 8b 06 31 d2 0f a3 05 6c 07 59 84 0f 92 c2 e8 12 65 b7 01 89 f0 e8 4b e9 2e 00 31 c0 83 c4 08 5e 5f 5b 5d c3 <0f> 0b b8 08 52 f5 83 e8 75 85 e6 ff 0f 0b b8 f8 51 f5 83 e8 69 85
All code
========
0: 83 7e 04 00 cmpl $0x0,0x4(%rsi)
4: 74 13 je 0x19
6: 8b 06 mov (%rsi),%eax
8: 31 d2 xor %edx,%edx
a: 0f a3 05 6c 07 59 84 bt %eax,-0x7ba6f894(%rip) # 0xffffffff8459077d
11: 0f 92 c2 setb %dl
14: e8 12 65 b7 01 call 0x1b7652b
19: 89 f0 mov %esi,%eax
1b: e8 4b e9 2e 00 call 0x2ee96b
20: 31 c0 xor %eax,%eax
22: 83 c4 08 add $0x8,%esp
25: 5e pop %rsi
26: 5f pop %rdi
27: 5b pop %rbx
28: 5d pop %rbp
29: c3 ret
2a:* 0f 0b ud2 <-- trapping instruction
2c: b8 08 52 f5 83 mov $0x83f55208,%eax
31: e8 75 85 e6 ff call 0xffffffffffe685ab
36: 0f 0b ud2
38: b8 f8 51 f5 83 mov $0x83f551f8,%eax
3d: e8 .byte 0xe8
3e: 69 .byte 0x69
3f: 85 .byte 0x85

Code starting with the faulting instruction ===========================================
0: 0f 0b ud2
2: b8 08 52 f5 83 mov $0x83f55208,%eax
7: e8 75 85 e6 ff call 0xffffffffffe68581
c: 0f 0b ud2
e: b8 f8 51 f5 83 mov $0x83f551f8,%eax
13: e8 .byte 0xe8
14: 69 .byte 0x69
15: 85 .byte 0x85
[ 2.436546][ T37] EAX: 00000003 EBX: 858ac510 ECX: 83e26f98 EDX: 83c50f80
[ 2.436546][ T37] ESI: 8500dfb0 EDI: 00000000 EBP: 858e1f68 ESP: 858e1f54
[ 2.436546][ T37] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010293
[ 2.436546][ T37] CR0: 80050033 CR2: 00000000 CR3: 047ae000 CR4: 000006b0
[ 2.436546][ T37] Call Trace:
[ 2.436546][ T37] kthread (kthread.c:436)
[ 2.436546][ T37] ? smpboot_unregister_percpu_thread (linux/list.h:261)
[ 2.436546][ T37] ? __do_trace_sched_kthread_stop_ret (trace/events/sched.h:38 (discriminator 13))
[ 2.436546][ T37] ret_from_fork (x86/kernel/process.c:158)
[ 2.436546][ T37] ? __do_trace_sched_kthread_stop_ret (trace/events/sched.h:38 (discriminator 13))
[ 2.436546][ T37] ret_from_fork_asm (x86/entry/entry_32.S:736)
[ 2.436546][ T37] entry_INT80_32 (x86/entry/entry_32.S:940)
[ 2.436546][ T37] Modules linked in:
[ 2.493945][ T37] ---[ end trace 0000000000000000 ]---
[ 2.496265][ T37] EIP: smpboot_thread_fn (smpboot.c:117)
[ 2.498528][ T37] Code: 83 7e 04 00 74 13 8b 06 31 d2 0f a3 05 6c 07 59 84 0f 92 c2 e8 12 65 b7 01 89 f0 e8 4b e9 2e 00 31 c0 83 c4 08 5e 5f 5b 5d c3 <0f> 0b b8 08 52 f5 83 e8 75 85 e6 ff 0f 0b b8 f8 51 f5 83 e8 69 85
All code
========
0: 83 7e 04 00 cmpl $0x0,0x4(%rsi)
4: 74 13 je 0x19
6: 8b 06 mov (%rsi),%eax
8: 31 d2 xor %edx,%edx
a: 0f a3 05 6c 07 59 84 bt %eax,-0x7ba6f894(%rip) # 0xffffffff8459077d
11: 0f 92 c2 setb %dl
14: e8 12 65 b7 01 call 0x1b7652b
19: 89 f0 mov %esi,%eax
1b: e8 4b e9 2e 00 call 0x2ee96b
20: 31 c0 xor %eax,%eax
22: 83 c4 08 add $0x8,%esp
25: 5e pop %rsi
26: 5f pop %rdi
27: 5b pop %rbx
28: 5d pop %rbp
29: c3 ret
2a:* 0f 0b ud2 <-- trapping instruction
2c: b8 08 52 f5 83 mov $0x83f55208,%eax
31: e8 75 85 e6 ff call 0xffffffffffe685ab
36: 0f 0b ud2
38: b8 f8 51 f5 83 mov $0x83f551f8,%eax
3d: e8 .byte 0xe8
3e: 69 .byte 0x69
3f: 85 .byte 0x85

Code starting with the faulting instruction ===========================================
0: 0f 0b ud2
2: b8 08 52 f5 83 mov $0x83f55208,%eax
7: e8 75 85 e6 ff call 0xffffffffffe68581
c: 0f 0b ud2
e: b8 f8 51 f5 83 mov $0x83f551f8,%eax
13: e8 .byte 0xe8
14: 69 .byte 0x69
15: 85 .byte 0x85

The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20261019/202610190859.d3459a50-lkp@xxxxxxxxx

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki