On Tue, Aug 26, 2025 at 04:47:22PM +0800, kernel test robot wrote:
>
> hi, Paul,
>
> the similar issue still exists on this dev.2025.08.21a branch.
> again, if the issue is already fixed on later branches, please just ignore.
> thanks
>
>
> Hello,
>
> kernel test robot noticed
> "WARNING:possible_circular_locking_dependency_detected" on:
>
> commit: 8bd9383727068a5a18acfecefbdfa44a7d6bd838 ("rcu: Re-implement RCU
> Tasks Trace in terms of SRCU-fast")
> https://github.com/paulmckrcu/linux dev.2025.08.21a
>
> in testcase: rcutorture
> version:
> with following parameters:
>
> runtime: 300s
> test: default
> torture_type: tasks-tracing
>
>
>
> config: x86_64-randconfig-003-20250824
> compiler: clang-20
> test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
>
> (please refer to attached dmesg/kmsg for entire log/backtrace)
Again, apologies for being slow, and thank you for your testing efforts.
Idiot here forgot about Tiny SRCU, so please see the end of this email
for an alleged fix. Does it do the trick for you?
Thanx, Paul
> 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.s...@intel.com>
> | Closes: https://lore.kernel.org/oe-lkp/202508261642.b15eefbb-...@intel.com
>
>
> [ 42.365933][ T393] WARNING: possible circular locking dependency detected
> [ 42.366428][ T393] 6.17.0-rc1-00035-g8bd938372706 #1 Tainted: G
> T
> [ 42.366985][ T393] ------------------------------------------------------
> [ 42.367490][ T393] rcu_torture_rea/393 is trying to acquire lock:
> [ 42.367952][ T393] ffffffffad41dc88
> (rcu_tasks_trace_srcu_struct.srcu_wq.lock){....}-{2:2}, at: swake_up_one
> (kernel/sched/swait.c:52 (discriminator 1))
> [ 42.368775][ T393]
> [ 42.368775][ T393] but task is already holding lock:
> [ 42.369278][ T393] ffff88813d1ff2e8 (&p->pi_lock){-.-.}-{2:2}, at:
> rcutorture_one_extend (kernel/rcu/rcutorture.c:?) rcutorture
> [ 42.370043][ T393]
> [ 42.370043][ T393] which lock already depends on the new lock.
> [ 42.370043][ T393]
> [ 42.370755][ T393]
> [ 42.370755][ T393] the existing dependency chain (in reverse order) is:
> [ 42.371388][ T393]
> [ 42.371388][ T393] -> #1 (&p->pi_lock){-.-.}-{2:2}:
> [ 42.371903][ T393] _raw_spin_lock_irqsave
> (include/linux/spinlock_api_smp.h:110 kernel/locking/spinlock.c:162)
> [ 42.372309][ T393] try_to_wake_up (include/linux/spinlock.h:557
> (discriminator 1) kernel/sched/core.c:4216 (discriminator 1))
> [ 42.372669][ T393] swake_up_locked (include/linux/list.h:111)
> [ 42.373029][ T393] swake_up_one (kernel/sched/swait.c:54 (discriminator 1))
> [ 42.373380][ T393] tasks_tracing_torture_read_unlock
> (include/linux/srcu.h:408 (discriminator 1) include/linux/rcupdate_trace.h:81
> (discriminator 1) kernel/rcu/rcutorture.c:1112 (discriminator 1)) rcutorture
> [ 42.373952][ T393] rcutorture_one_extend (kernel/rcu/rcutorture.c:2141)
> rcutorture
> [ 42.374452][ T393] rcu_torture_one_read_end (kernel/rcu/rcutorture.c:2357)
> rcutorture
> [ 42.374976][ T393] rcu_torture_one_read (kernel/rcu/rcutorture.c:?)
> rcutorture
> [ 42.375460][ T393] rcu_torture_reader (kernel/rcu/rcutorture.c:2443)
> rcutorture
> [ 42.375920][ T393] kthread (kernel/kthread.c:465)
> [ 42.376241][ T393] ret_from_fork (arch/x86/kernel/process.c:154)
> [ 42.376603][ T393] ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
> [ 42.376973][ T393]
> [ 42.376973][ T393] -> #0
> (rcu_tasks_trace_srcu_struct.srcu_wq.lock){....}-{2:2}:
> [ 42.377657][ T393] __lock_acquire (kernel/locking/lockdep.c:3166)
> [ 42.378031][ T393] lock_acquire (kernel/locking/lockdep.c:5868)
> [ 42.378378][ T393] _raw_spin_lock_irqsave
> (include/linux/spinlock_api_smp.h:110 kernel/locking/spinlock.c:162)
> [ 42.378794][ T393] swake_up_one (kernel/sched/swait.c:52 (discriminator 1))
> [ 42.379152][ T393] tasks_tracing_torture_read_unlock
> (include/linux/srcu.h:408 (discriminator 1) include/linux/rcupdate_trace.h:81
> (discriminator 1) kernel/rcu/rcutorture.c:1112 (discriminator 1)) rcutorture
> [ 42.379714][ T393] rcutorture_one_extend (kernel/rcu/rcutorture.c:2141)
> rcutorture
> [ 42.380217][ T393] rcu_torture_one_read_end (kernel/rcu/rcutorture.c:2357)
> rcutorture
> [ 42.380731][ T393] rcu_torture_one_read (kernel/rcu/rcutorture.c:?)
> rcutorture
> [ 42.381220][ T393] rcu_torture_reader (kernel/rcu/rcutorture.c:2443)
> rcutorture
> [ 42.381714][ T393] kthread (kernel/kthread.c:465)
> [ 42.382060][ T393] ret_from_fork (arch/x86/kernel/process.c:154)
> [ 42.382420][ T393] ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
> [ 42.382796][ T393]
> [ 42.382796][ T393] other info that might help us debug this:
> [ 42.382796][ T393]
> [ 42.383515][ T393] Possible unsafe locking scenario:
> [ 42.383515][ T393]
> [ 42.384052][ T393] CPU0 CPU1
> [ 42.384428][ T393] ---- ----
> [ 42.384799][ T393] lock(&p->pi_lock);
> [ 42.385083][ T393]
> lock(rcu_tasks_trace_srcu_struct.srcu_wq.lock);
> [ 42.385707][ T393] lock(&p->pi_lock);
> [ 42.386180][ T393] lock(rcu_tasks_trace_srcu_struct.srcu_wq.lock);
> [ 42.386663][ T393]
> [ 42.386663][ T393] *** DEADLOCK ***
> [ 42.386663][ T393]
> [ 42.387236][ T393] 1 lock held by rcu_torture_rea/393:
> [ 42.387626][ T393] #0: ffff88813d1ff2e8 (&p->pi_lock){-.-.}-{2:2}, at:
> rcutorture_one_extend (kernel/rcu/rcutorture.c:?) rcutorture
> [ 42.388419][ T393]
> [ 42.388419][ T393] stack backtrace:
> [ 42.388852][ T393] CPU: 0 UID: 0 PID: 393 Comm: rcu_torture_rea Tainted:
> G T 6.17.0-rc1-00035-g8bd938372706 #1 PREEMPT(full)
> [ 42.389758][ T393] Tainted: [T]=RANDSTRUCT
> [ 42.390057][ T393] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> [ 42.390786][ T393] Call Trace:
> [ 42.391020][ T393] <TASK>
> [ 42.391225][ T393] dump_stack_lvl (lib/dump_stack.c:123 (discriminator 2))
> [ 42.391544][ T393] print_circular_bug (kernel/locking/lockdep.c:2045)
> [ 42.391898][ T393] check_noncircular (kernel/locking/lockdep.c:?)
> [ 42.392242][ T393] __lock_acquire (kernel/locking/lockdep.c:3166)
> [ 42.392594][ T393] ? __schedule (kernel/sched/sched.h:1531 (discriminator 1)
> kernel/sched/core.c:6969 (discriminator 1))
> [ 42.392930][ T393] ? lock_release (kernel/locking/lockdep.c:470
> (discriminator 3))
> [ 42.393272][ T393] ? swake_up_one (kernel/sched/swait.c:52 (discriminator
> 1))
> [ 42.393610][ T393] lock_acquire (kernel/locking/lockdep.c:5868)
> [ 42.393930][ T393] ? swake_up_one (kernel/sched/swait.c:52 (discriminator
> 1))
> [ 42.394264][ T393] _raw_spin_lock_irqsave
> (include/linux/spinlock_api_smp.h:110 kernel/locking/spinlock.c:162)
> [ 42.394640][ T393] ? swake_up_one (kernel/sched/swait.c:52 (discriminator
> 1))
> [ 42.394969][ T393] swake_up_one (kernel/sched/swait.c:52 (discriminator 1))
> [ 42.395281][ T393] tasks_tracing_torture_read_unlock
> (include/linux/srcu.h:408 (discriminator 1) include/linux/rcupdate_trace.h:81
> (discriminator 1) kernel/rcu/rcutorture.c:1112 (discriminator 1)) rcutorture
> [ 42.395814][ T393] rcutorture_one_extend (kernel/rcu/rcutorture.c:2141)
> rcutorture
> [ 42.396276][ T393] rcu_torture_one_read_end (kernel/rcu/rcutorture.c:2357)
> rcutorture
> [ 42.396756][ T393] rcu_torture_one_read (kernel/rcu/rcutorture.c:?)
> rcutorture
> [ 42.397219][ T393] ? __cfi_rcu_torture_reader (kernel/rcu/rcutorture.c:2426)
> rcutorture
> [ 42.397690][ T393] rcu_torture_reader (kernel/rcu/rcutorture.c:2443)
> rcutorture
> [ 42.398126][ T393] ? __cfi_rcu_torture_timer (kernel/rcu/rcutorture.c:2405)
> rcutorture
> [ 42.398565][ T393] kthread (kernel/kthread.c:465)
> [ 42.398857][ T393] ? __cfi_kthread (kernel/kthread.c:412)
> [ 42.399169][ T393] ret_from_fork (arch/x86/kernel/process.c:154)
> [ 42.399491][ T393] ? __cfi_kthread (kernel/kthread.c:412)
> [ 42.399815][ T393] ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
> [ 42.400151][ T393] </TASK>
>
>
> The kernel config and materials to reproduce are available at:
> https://download.01.org/0day-ci/archive/20250826/202508261642.b15eefbb-...@intel.com
>
>
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
------------------------------------------------------------------------
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 6e9fe2ce1075d5..db63378f062051 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -106,7 +106,7 @@ void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
preempt_enable();
- if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task())
+ if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task() &&
!irqs_disabled())
swake_up_one(&ssp->srcu_wq);
}
EXPORT_SYMBOL_GPL(__srcu_read_unlock);
