Re: [PATCH 10/19] sched/fair: Prioritize tasks preferring destination LLC during balancing

[kernel test robot <oliver.sang@intel.com>]

Hello,

kernel test robot noticed "UBSAN:array-index-out-of-bounds_in_kernel/sched/fair.c" on:

commit: a9872e774986636a909d5cc6f6bde8b44add9f33 ("[PATCH 10/19] sched/fair: Prioritize tasks preferring destination LLC during balancing")
url: https://github.com/intel-lab-lkp/linux/commits/Tim-Chen/sched-fair-Add-infrastructure-for-cache-aware-load-balancing/20251012-022248
base: https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git 45b7f780739a3145aeef24d2dfa02517a6c82ed6
patch link: https://lore.kernel.org/all/ca1946de63ad9f0ae99e079a74d70c55879cc0b6.1760206683.git.tim.c.chen@linux.intel.com/
patch subject: [PATCH 10/19] sched/fair: Prioritize tasks preferring destination LLC during balancing

in testcase: boot

config: i386-randconfig-003-20251012
compiler: clang-20
test machine: qemu-system-i386 -enable-kvm -cpu SandyBridge -smp 2 -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 <oliver.sang@intel.com>
| Closes: https://lore.kernel.org/oe-lkp/202510151514.652b80d2-lkp@intel.com


[    0.527179][    T2] ------------[ cut here ]------------
[    0.527563][    T2] UBSAN: array-index-out-of-bounds in kernel/sched/fair.c:10965:6
[    0.527563][    T2] index -1 is out of range for type 'unsigned int[8]'
[    0.527563][    T2] CPU: 0 UID: 0 PID: 2 Comm: kthreadd Not tainted 6.17.0-rc4-00027-ga9872e774986 #1 PREEMPTLAZY
[    0.527563][    T2] Call Trace:
[    0.527563][    T2]  ? __dump_stack (lib/dump_stack.c:95)
[    0.527563][    T2]  ? dump_stack_lvl (lib/dump_stack.c:123)
[    0.527563][    T2]  ? ubsan_epilogue.llvm.14679606394994327670 (lib/dump_stack.c:129 lib/ubsan.c:233)
[    0.527563][    T2]  ? __ubsan_handle_out_of_bounds (lib/ubsan.c:?)
[    0.527563][    T2]  ? sched_balance_rq (kernel/sched/fair.c:?)
[    0.527563][    T2]  ? sched_balance_newidle (kernel/sched/fair.c:13514)
[    0.527563][    T2]  ? pick_next_task_fair (kernel/sched/fair.c:9328)
[    0.527563][    T2]  ? dequeue_task (kernel/sched/core.c:2136)
[    0.527563][    T2]  ? __pick_next_task (kernel/sched/core.c:5983)
[    0.527563][    T2]  ? __schedule (kernel/sched/core.c:?)
[    0.527563][    T2]  ? schedule (kernel/sched/core.c:7025 kernel/sched/core.c:7039)
[    0.527563][    T2]  ? kthreadd (kernel/kthread.c:835)
[    0.527563][    T2]  ? kthread_stop_put (kernel/kthread.c:818)
[    0.527563][    T2]  ? ret_from_fork (arch/x86/kernel/process.c:154)
[    0.527563][    T2]  ? kthread_stop_put (kernel/kthread.c:818)
[    0.527563][    T2]  ? debug_smp_processor_id (lib/smp_processor_id.c:58)
[    0.527563][    T2]  ? kthread_stop_put (kernel/kthread.c:818)
[    0.527563][    T2]  ? ret_from_fork_asm (arch/x86/entry/entry_32.S:737)
[    0.527563][    T2]  ? entry_INT80_32 (arch/x86/entry/entry_32.S:945)
[    0.527563][    T2] ---[ end trace ]---


The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20251015/202510151514.652b80d2-lkp@intel.com



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