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

[Paul E. McKenney]

On Tue, Oct 20, 2026 at 03:01:27PM -0700, Paul E. McKenney wrote:
> 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!

Wait, Joel is doing the next merge window, not me!

Joel, please make that be:

Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

I will drop it from my tree, apologies for my confusion!

							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