* [tip:sched/core] [sched/fair] c9d93a73ce: WARNING:suspicious_RCU_usage
@ 2026-05-23 13:27 kernel test robot
2026-05-25 1:53 ` Chen, Yu C
0 siblings, 1 reply; 4+ messages in thread
From: kernel test robot @ 2026-05-23 13:27 UTC (permalink / raw)
To: Andrea Righi
Cc: oe-lkp, lkp, linux-kernel, x86, Peter Zijlstra, K Prateek Nayak,
Vincent Guittot, aubrey.li, yu.c.chen, oliver.sang
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 <oliver.sang@intel.com>
| Closes: https://lore.kernel.org/oe-lkp/202605232131.cfcd45a2-lkp@intel.com
[ 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/20260523/202605232131.cfcd45a2-lkp@intel.com
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [tip:sched/core] [sched/fair] c9d93a73ce: WARNING:suspicious_RCU_usage
2026-05-23 13:27 [tip:sched/core] [sched/fair] c9d93a73ce: WARNING:suspicious_RCU_usage kernel test robot
@ 2026-05-25 1:53 ` Chen, Yu C
2026-05-25 4:24 ` Andrea Righi
0 siblings, 1 reply; 4+ messages in thread
From: Chen, Yu C @ 2026-05-25 1:53 UTC (permalink / raw)
To: kernel test robot, Andrea Righi
Cc: oe-lkp, lkp, linux-kernel, x86, Peter Zijlstra, K Prateek Nayak,
Vincent Guittot, aubrey.li
On 5/23/2026 9:27 PM, kernel test robot wrote:
>
> [ 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]
sched_cpu_deactivate() does not hold RCU read lock, nor are
preemption/IRQs/BH disabled,
how about this:
static void set_cpu_sd_state_busy(int cpu)
{
struct sched_domain *sd;
- sd = rcu_dereference_all(per_cpu(sd_llc, cpu));
+ sd = rcu_dereference_all_check(per_cpu(sd_llc, cpu),
+ lockdep_is_cpus_held());
/*
* sd->nohz_idle only pairs with nr_busy_cpus on sd->shared; if
this
@@ -12815,7 +12817,8 @@ void nohz_balance_exit_idle(struct rq *rq)
static void set_cpu_sd_state_idle(int cpu)
{
struct sched_domain *sd;
- sd = rcu_dereference_all(per_cpu(sd_llc, cpu));
+ sd = rcu_dereference_all_check(per_cpu(sd_llc, cpu),
+ lockdep_is_cpus_held());
/* See set_cpu_sd_state_busy(): nohz_idle is only used with
sd->shared. */
if (!sd || !sd->shared || sd->nohz_idle)
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [tip:sched/core] [sched/fair] c9d93a73ce: WARNING:suspicious_RCU_usage
2026-05-25 1:53 ` Chen, Yu C
@ 2026-05-25 4:24 ` Andrea Righi
2026-05-25 8:08 ` Chen, Yu C
0 siblings, 1 reply; 4+ messages in thread
From: Andrea Righi @ 2026-05-25 4:24 UTC (permalink / raw)
To: Chen, Yu C
Cc: kernel test robot, oe-lkp, lkp, linux-kernel, x86, Peter Zijlstra,
K Prateek Nayak, Vincent Guittot, aubrey.li
Hello,
On Mon, May 25, 2026 at 09:53:22AM +0800, Chen, Yu C wrote:
> On 5/23/2026 9:27 PM, kernel test robot wrote:
>
> >
> > [ 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]
This should be fixed by
https://lore.kernel.org/all/20260522092523.2046095-1-arighi@nvidia.com/
Thanks,
-Andrea
>
> sched_cpu_deactivate() does not hold RCU read lock, nor are
> preemption/IRQs/BH disabled,
> how about this:
> static void set_cpu_sd_state_busy(int cpu)
> {
> struct sched_domain *sd;
> - sd = rcu_dereference_all(per_cpu(sd_llc, cpu));
> + sd = rcu_dereference_all_check(per_cpu(sd_llc, cpu),
> + lockdep_is_cpus_held());
>
> /*
> * sd->nohz_idle only pairs with nr_busy_cpus on sd->shared; if this
> @@ -12815,7 +12817,8 @@ void nohz_balance_exit_idle(struct rq *rq)
> static void set_cpu_sd_state_idle(int cpu)
> {
> struct sched_domain *sd;
> - sd = rcu_dereference_all(per_cpu(sd_llc, cpu));
> + sd = rcu_dereference_all_check(per_cpu(sd_llc, cpu),
> + lockdep_is_cpus_held());
>
> /* See set_cpu_sd_state_busy(): nohz_idle is only used with
> sd->shared. */
> if (!sd || !sd->shared || sd->nohz_idle)
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [tip:sched/core] [sched/fair] c9d93a73ce: WARNING:suspicious_RCU_usage
2026-05-25 4:24 ` Andrea Righi
@ 2026-05-25 8:08 ` Chen, Yu C
0 siblings, 0 replies; 4+ messages in thread
From: Chen, Yu C @ 2026-05-25 8:08 UTC (permalink / raw)
To: Andrea Righi
Cc: kernel test robot, oe-lkp, lkp, linux-kernel, x86, Peter Zijlstra,
K Prateek Nayak, Vincent Guittot, aubrey.li
On 5/25/2026 12:24 PM, Andrea Righi wrote:
> Hello,
>
> On Mon, May 25, 2026 at 09:53:22AM +0800, Chen, Yu C wrote:
>> On 5/23/2026 9:27 PM, kernel test robot wrote:
>>
>>>
>>> [ 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]
>
> This should be fixed by
> https://lore.kernel.org/all/20260522092523.2046095-1-arighi@nvidia.com/
>
Got it, thanks for the fix!
thanks,
Chenyu
^ permalink raw reply [flat|nested] 4+ messages in thread
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2026-05-23 13:27 [tip:sched/core] [sched/fair] c9d93a73ce: WARNING:suspicious_RCU_usage kernel test robot
2026-05-25 1:53 ` Chen, Yu C
2026-05-25 4:24 ` Andrea Righi
2026-05-25 8:08 ` Chen, Yu C
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