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[PATCH] srcutiny: Add lockdep and early-boot checks to synchronize_srcu_atomic()

Kunwu Chan posted 1 patch 1 week, 6 days ago 
kernel/rcu/srcutiny.c | 6 ++++++
1 file changed, 6 insertions(+)
[PATCH] srcutiny: Add lockdep and early-boot checks to synchronize_srcu_atomic()
Posted by Kunwu Chan 1 week, 6 days ago 
Add the RCU_LOCKDEP_WARN and early-boot check that the Tree version
gained, srcu_lock_sync() was already present.

Suggested-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 kernel/rcu/srcutiny.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 99f8bfd98b04..76411562366f 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -361,6 +361,12 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
 
 	srcu_lock_sync(&ssp->dep_map);
 
+	RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
+			 "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
+
+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+		return;
+
 	if (IS_ENABLED(CONFIG_PREEMPTION))
 		synchronize_rcu(); // Needed for RCU Tasks Trace to imply RCU grace period.
 				   // And in Tiny RCU, it is near zero cost and doesn't block.
-- 
2.43.0
Re: [PATCH] srcutiny: Add lockdep and early-boot checks to synchronize_srcu_atomic()
Posted by Bradley Morgan 1 week, 6 days ago 
On 11 September 2026 17:09:13 BST, Kunwu Chan <kunwu.chan@gmail.com> wrote:
>Add the RCU_LOCKDEP_WARN and early-boot check that the Tree version
>gained, srcu_lock_sync() was already present.
>
>Suggested-by: Zqiang <qiang.zhang@linux.dev>

Ok.

Reviewed-by: Bradley Morgan <brads@mainlining.org>


>Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
>---
> kernel/rcu/srcutiny.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
>diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
>index 99f8bfd98b04..76411562366f 100644
>--- a/kernel/rcu/srcutiny.c
>+++ b/kernel/rcu/srcutiny.c
>@@ -361,6 +361,12 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
> 
> 	srcu_lock_sync(&ssp->dep_map);
> 
>+	RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
>+			 "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
>+
>+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
>+		return;
>+

Wow!

> 	if (IS_ENABLED(CONFIG_PREEMPTION))
> 		synchronize_rcu(); // Needed for RCU Tasks Trace to imply RCU grace period.
> 				   // And in Tiny RCU, it is near zero cost and doesn't block.
>

--- Thanks!
https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/
Re: [PATCH] srcutiny: Add lockdep and early-boot checks to synchronize_srcu_atomic()
Posted by Paul E. McKenney 1 week, 6 days ago 
On Fri, Sep 11, 2026 at 10:18:04PM +0100, Bradley Morgan wrote:
> On 11 September 2026 17:09:13 BST, Kunwu Chan <kunwu.chan@gmail.com> wrote:
> >Add the RCU_LOCKDEP_WARN and early-boot check that the Tree version
> >gained, srcu_lock_sync() was already present.
> >
> >Suggested-by: Zqiang <qiang.zhang@linux.dev>
> 
> Ok.
> 
> Reviewed-by: Bradley Morgan <brads@mainlining.org>

Applied, thank you!

> >Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
> >---
> > kernel/rcu/srcutiny.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> >diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> >index 99f8bfd98b04..76411562366f 100644
> >--- a/kernel/rcu/srcutiny.c
> >+++ b/kernel/rcu/srcutiny.c
> >@@ -361,6 +361,12 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
> > 
> > 	srcu_lock_sync(&ssp->dep_map);
> > 
> >+	RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
> >+			 "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
> >+
> >+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> >+		return;
> >+
> 
> Wow!

If you think that this one is fun, take a look at the implementation of
synchronize_rcu() in kernel/rcu/tiny.c.  ;-)

							Thanx, Paul

> > 	if (IS_ENABLED(CONFIG_PREEMPTION))
> > 		synchronize_rcu(); // Needed for RCU Tasks Trace to imply RCU grace period.
> > 				   // And in Tiny RCU, it is near zero cost and doesn't block.
> >
> 
> --- Thanks!
> https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/
Re: [PATCH] srcutiny: Add lockdep and early-boot checks to synchronize_srcu_atomic()
Posted by Bradley Morgan 1 week, 6 days ago 
On 12 September 2026 00:12:25 BST, "Paul E. McKenney" <paulmck@kernel.org>
wrote:
>On Fri, Sep 11, 2026 at 10:18:04PM +0100, Bradley Morgan wrote:
>> On 11 September 2026 17:09:13 BST, Kunwu Chan <kunwu.chan@gmail.com>
>wrote:
>> >Add the RCU_LOCKDEP_WARN and early-boot check that the Tree version
>> >gained, srcu_lock_sync() was already present.
>> >
>> >Suggested-by: Zqiang <qiang.zhang@linux.dev>
>> 
>> Ok.
>> 
>> Reviewed-by: Bradley Morgan <brads@mainlining.org>
>
>Applied, thank you!
>
>> >Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
>> >---
>> > kernel/rcu/srcutiny.c | 6 ++++++
>> > 1 file changed, 6 insertions(+)
>> >
>> >diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
>> >index 99f8bfd98b04..76411562366f 100644
>> >--- a/kernel/rcu/srcutiny.c
>> >+++ b/kernel/rcu/srcutiny.c
>> >@@ -361,6 +361,12 @@ void synchronize_srcu_atomic(struct srcu_struct
>*ssp)
>> > 
>> > 	srcu_lock_sync(&ssp->dep_map);
>> > 
>> >+	RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
>> >+			 "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
>> >+
>> >+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
>> >+		return;
>> >+
>> 
>> Wow!
>
>If you think that this one is fun, take a look at the implementation of
>synchronize_rcu() in kernel/rcu/tiny.c.  ;-)


void synchronize_rcu(void)
{
    RCU_LOCKDEP_WARN(...);
    preempt_disable();
    WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2);
    preempt_enable();
}

Hah!

>
>							Thanx, Paul
>
>> > 	if (IS_ENABLED(CONFIG_PREEMPTION))
>> > 		synchronize_rcu(); // Needed for RCU Tasks Trace to imply RCU grace period.
>> > 				   // And in Tiny RCU, it is near zero cost and doesn't block.
>> >
>> 
>> --- Thanks!
>>
>https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/

--- Thanks!
https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/
Re: [PATCH] srcutiny: Add lockdep and early-boot checks to synchronize_srcu_atomic()
Posted by Paul E. McKenney 1 week, 6 days ago 
On Sat, Sep 12, 2026 at 12:09:13AM +0800, Kunwu Chan wrote:
> Add the RCU_LOCKDEP_WARN and early-boot check that the Tree version
> gained, srcu_lock_sync() was already present.
> 
> Suggested-by: Zqiang <qiang.zhang@linux.dev>
> Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>

Queued for testing and review, thank you both!

							Thanx, Paul

> ---
>  kernel/rcu/srcutiny.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index 99f8bfd98b04..76411562366f 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -361,6 +361,12 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
>  
>  	srcu_lock_sync(&ssp->dep_map);
>  
> +	RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
> +			 "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
> +
> +	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> +		return;
> +
>  	if (IS_ENABLED(CONFIG_PREEMPTION))
>  		synchronize_rcu(); // Needed for RCU Tasks Trace to imply RCU grace period.
>  				   // And in Tiny RCU, it is near zero cost and doesn't block.
> -- 
> 2.43.0
>

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