rcutorture: Fix suspicious rcu_dereference_check() usage for trivial-preempt

PATCH In review Zqiang 4 participants 5 messages Oct 20

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RCU Torture-test modules

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Zqiang

author reviewer

2026-10-20 09:49 UTC #0 lore raw

PATCH 1/1 rcutorture: Fix suspicious rcu_dereference_check() usage for trivial-preempt

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")

Signed-off-by Zqiang <[email protected]>

---
 kernel/rcu/rcutorture.c | 1 -
 1 file changed, 1 deletion(-)

kernel/rcu/rcutorture.c +0 -1

index 92ff197f4789..1bbf8192786a 100644
@@ -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,

Signature · 1 line

2.17.1

Bradley Morgan

Reviewed-by on v1 1/1

2026-10-20 15:07 UTC #1 lore raw

Quoted 20 lines · Zqiang

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.

Quoted 1 line

Fixes c6f4e552e1ea ("rcutorture: Add a textbook-style trivial preemptible RCU")

Looks ok to me.

Reviewed-by Bradley Morgan <[email protected]>

Quoted 11 lines

Signed-off-by Zqiang <[email protected]>
---
kernel/rcu/rcutorture.c | 1 -
1 file changed, 1 deletion(-)
kernel/rcu/rcutorture.c +0 -0
index 92ff197f4789..1bbf8192786a 100644

kernel/rcu/rcutorture.c static struct rcu_torture_ops trivial_preempt_ops = { · line 1169

Quoted 7 lines

kernel/rcu/rcutorture.c +0 -1

@@ -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

Paul E. McKenney

maintainer

2026-10-20 22:01 UTC #2 lore raw

Quoted 21 lines · Bradley Morgan

Quoted 20 lines · Zqiang
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.

Quoted 7 lines

Quoted 1 line
Fixes c6f4e552e1ea ("rcutorture: Add a textbook-style trivial preemptible RCU")
Looks ok to me.
Reviewed-by Bradley Morgan <[email protected]>
Quoted 1 line
Signed-off-by Zqiang <[email protected]>

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

Quoted 20 lines

Quoted 10 lines
---
kernel/rcu/rcutorture.c | 1 -
1 file changed, 1 deletion(-)
kernel/rcu/rcutorture.c +0 -0
index 92ff197f4789..1bbf8192786a 100644
kernel/rcu/rcutorture.c static struct rcu_torture_ops trivial_preempt_ops = { · line 1169
Quoted 7 lines
kernel/rcu/rcutorture.c +0 -1
@@ -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

Paul E. McKenney

maintainer Reviewed-by Tested-by

2026-10-20 22:03 UTC #3 lore raw

Quoted 24 lines · Paul E. McKenney

Quoted 23 lines · Bradley Morgan
Quoted 21 lines · Zqiang
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")

Quoted 8 lines

Quoted 5 lines
Looks ok to me.
Reviewed-by Bradley Morgan <[email protected]>
Quoted 1 line
Signed-off-by Zqiang <[email protected]>
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 <[email protected]>

Tested-by Paul E. McKenney <[email protected]>

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

Thanx, Paul

Quoted 20 lines

Quoted 20 lines
Quoted 10 lines
---
kernel/rcu/rcutorture.c | 1 -
1 file changed, 1 deletion(-)
kernel/rcu/rcutorture.c +0 -0
index 92ff197f4789..1bbf8192786a 100644
kernel/rcu/rcutorture.c static struct rcu_torture_ops trivial_preempt_ops = { · line 1169
Quoted 7 lines
kernel/rcu/rcutorture.c +0 -1
@@ -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

Joel Fernandes

maintainer

2026-10-20 22:20 UTC #4 lore raw

Quoted 34 lines · Paul E. McKenney

Quoted 24 lines · Paul E. McKenney
Quoted 23 lines · Bradley Morgan
Quoted 21 lines · Zqiang
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")
Quoted 8 lines
Quoted 5 lines
Looks ok to me.
Reviewed-by Bradley Morgan <[email protected]>
Quoted 1 line
Signed-off-by Zqiang <[email protected]>
And it works here, thank you both. I have queued this, and thank you Zqiang for thinking to test trivial-preempt with lockdep enabled!

Quoted 8 lines

Wait, Joel is doing the next merge window, not me!
Joel, please make that be:
Reviewed-by Paul E. McKenney <[email protected]>
Tested-by Paul E. McKenney <[email protected]>
I will drop it from my tree, apologies for my confusion!

Applied for 7.5 for further testing, thanks!

thanks,

Joel Fernandes