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

[Bradley Morgan]

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>
>---
> 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