Re: [PATCH] rcutorture: Fix suspicious rcu_dereference_check() usage for trivial-preempt

[Paul E. McKenney]

On Tue, Oct 20, 2026 at 04:06:49PM +0100, Bradley Morgan wrote:
> On 20 October 2026 10:49:07 BST, Zqiang <qiang.zhang@xxxxxxxxx> wrote:
> >Running the trivial-preempt flavor triggers a lockdep "suspicious RCU
> >usage" warning from rcu_torture_one_read_start():
> >
> >WARNING: suspicious RCU usage
> >kernel/rcu/rcutorture.c:2581 suspicious rcu_dereference_check() usage!
> >...
> >lockdep_rcu_suspicious
> >rcu_torture_one_read_start
> >rcu_torture_one_read
> >rcu_torture_reader
> >
> >The trivial-preempt flavor .readlock_held is set to
> >torture_readlock_not_held(),
> >which check RCU-bh/RCU-sched critical sections. however, it's read lock
> >just increments current->rcu_trivial_preempt_nesting, it's not also RCU
> >read critical sections. the rcu_dereference_check() condition is therefore
> >false, and lockdep report warnings. this commit therefore drop
> >.readlock_held
> >callback to avoid this lockdep warnings.
> >
> >Fixes: c6f4e552e1ea ("rcutorture: Add a textbook-style trivial preemptible RCU")
> 
> Looks ok to me.
> 
> Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>
> 
> >Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxx>

And it works here, thank you both.  I have queued this, and thank you
Zqiang for thinking to test trivial-preempt with lockdep enabled!

							Thanx, Paul

> >---
> > kernel/rcu/rcutorture.c | 1 -
> > 1 file changed, 1 deletion(-)
> >
> >diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> >index 92ff197f4789..1bbf8192786a 100644
> >--- a/kernel/rcu/rcutorture.c
> >+++ b/kernel/rcu/rcutorture.c
> >@@ -1164,7 +1164,6 @@ static struct rcu_torture_ops trivial_preempt_ops = {
> > 	.readlock	= rcu_torture_read_lock_trivial_preempt,
> > 	.read_delay	= rcu_read_delay,  // just reuse rcu's version.
> > 	.readunlock	= rcu_torture_read_unlock_trivial_preempt,
> >-	.readlock_held	= torture_readlock_not_held,
> > 	.get_gp_seq	= rcu_no_completed,
> > 	.sync		= synchronize_rcu_trivial_preempt,
> > 	.exp_sync	= synchronize_rcu_trivial_preempt,
> >
> 
> --- Thanks!
> "I'm not a very positive person" - Linus torvalds