[tip:sched/core] [sched/fair] c9d93a73ce: WARNING:suspicious_RCU_usage

Hello,

kernel test robot noticed "WARNING:suspicious_RCU_usage" on:

commit: c9d93a73ce871ca32caf9308562501290b64b955 ("sched/fair: Drop redundant RCU read lock in NOHZ kick path")
https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git sched/core


in testcase: rcutorture
version: 
with following parameters:

	runtime: 300s
	test: cpuhotplug
	torture_type: tasks-rude



config: x86_64-randconfig-001-20260521
compiler: clang-20
test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 32G

(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 <[email protected]>
| Closes: https://lore.kernel.org/oe-lkp/[email protected]



[  102.159951][   T23]
[  102.160730][   T23] =============================
[  102.162072][   T23] WARNING: suspicious RCU usage
[  102.163398][   T23] 7.1.0-rc2-00011-gc9d93a73ce87 #1 Not tainted
[  102.165064][   T23] -----------------------------
[  102.167687][   T23] kernel/sched/fair.c:12793 suspicious rcu_dereference_check() usage!
[  102.169994][   T23]
[  102.169994][   T23] other info that might help us debug this:
[  102.169994][   T23]
[  102.169994][   T23] other info that might help us debug this:
[  102.169994][   T23]
[  102.169994][   T23] other info that might help us debug this:
[  102.169994][   T23]
[  102.175418][   T23]
[  102.175418][   T23] rcu_scheduler_active = 2, debug_locks = 1
[  102.175418][   T23]
[  102.175418][   T23] rcu_scheduler_active = 2, debug_locks = 1
[  102.175418][   T23]
[  102.175418][   T23] rcu_scheduler_active = 2, debug_locks = 1
[  102.180431][   T23] 2 locks held by cpuhp/1/23:
[  102.182158][   T23]  #0: ffffffff872eadf0 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun (cpu.c:545 cpu.c:1085)
[  102.184843][   T23]  #1: ffffffff872eaf20 (cpuhp_state-down){+.+.}-{0:0}, at: cpuhp_thread_fun (cpu.c:545 cpu.c:1085)
[  102.187589][   T23]
[  102.187589][   T23] stack backtrace:
[  102.187589][   T23]
[  102.187589][   T23] stack backtrace:
[  102.187589][   T23]
[  102.187589][   T23] stack backtrace:
[  102.189233][   T23] CPU: 1 UID: 0 PID: 23 Comm: cpuhp/1 Not tainted 7.1.0-rc2-00011-gc9d93a73ce87 #1 PREEMPT
[  102.189241][   T23] Call Trace:
[  102.189245][   T23]  <TASK>
[  102.189251][   T23]  __dump_stack (dump_stack.c:94)
[  102.189260][   T23]  dump_stack_lvl (dump_stack.c:120)
[  102.189266][   T23]  dump_stack (dump_stack.c:129)
[  102.189270][   T23]  lockdep_rcu_suspicious (locking/lockdep.c:6876)
[  102.189279][   T23]  set_cpu_sd_state_busy (sched/fair.c:12793)
[  102.189286][   T23]  nohz_balance_exit_idle (sched/fair.c:12812)
[  102.189293][   T23]  sched_cpu_deactivate (sched/core.c:8677)
[  102.189300][   T23]  ? trace_cpuhp_enter (trace/events/cpuhp.h:10)
[  102.189305][   T23]  ? balance_push_set (sched/sched.h:?)
[  102.189312][   T23]  cpuhp_invoke_callback (cpu.c:194)
[  102.189315][   T23]  ? lock_acquire (locking/lockdep.c:5868)
[  102.189321][   T23]  ? cpuhp_thread_fun (cpu.c:545 cpu.c:1085)
[  102.189326][   T23]  ? lock_acquire (locking/lockdep.c:5868)
[  102.189337][   T23]  cpuhp_thread_fun (cpu.c:1109)
[  102.189341][   T23]  ? cpuhp_thread_fun (cpu.c:545 cpu.c:1085)
[  102.189350][   T23]  ? cpuhp_should_run (cpu.c:?)
[  102.189354][   T23]  smpboot_thread_fn (smpboot.c:160)
[  102.189364][   T23]  ? smpboot_thread_fn (smpboot.c:?)
[  102.189373][   T23]  kthread (kthread.c:436)
[  102.189379][   T23]  ? smpboot_unregister_percpu_thread (smpboot.c:321)
[  102.189385][   T23]  ? kthread_unuse_mm (kthread.c:?)
[  102.189392][   T23]  ret_from_fork (x86/kernel/process.c:158)
[  102.189397][   T23]  ? kthread_unuse_mm (kthread.c:?)
[  102.189402][   T23]  ret_from_fork_asm (x86/entry/entry_64.S:245)
[  102.189416][   T23]  </TASK>


The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20260523/[email protected]



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https://github.com/intel/lkp-tests/wiki