[PATCH v3] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if_needed()

[PATCH v3] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if_needed()

[Zqiang]

Currently, the srcu_gp_start_if_needed() is always be invoked in
preempt disable's critical section, this commit therefore remove
redundant preempt_disable/enable() in srcu_gp_start_if_needed()
and adds a call to lockdep_assert_preemption_disabled() in order
to enable lockdep to diagnose mistaken invocations of this function
from preempts-enabled code.

Fixes: 65b4a59557f6 ("srcu: Make Tiny SRCU explicitly disable preemption")
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/srcutiny.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index b52ec45698e8..3450c3751ef7 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -181,10 +181,9 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
 {
 	unsigned long cookie;
 
-	preempt_disable();  // Needed for PREEMPT_LAZY
+	lockdep_assert_preemption_disabled(); // Needed for PREEMPT_LAZY
 	cookie = get_state_synchronize_srcu(ssp);
 	if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) {
-		preempt_enable();
 		return;
 	}
 	WRITE_ONCE(ssp->srcu_idx_max, cookie);
@@ -194,7 +193,6 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
 		else if (list_empty(&ssp->srcu_work.entry))
 			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
 	}
-	preempt_enable();
 }
 
 /*
-- 
2.48.1

Re: [PATCH v3] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if_needed()

[Paul E. McKenney]

On Thu, Sep 11, 2025 at 08:51:55PM +0800, Zqiang wrote:
> Currently, the srcu_gp_start_if_needed() is always be invoked in
> preempt disable's critical section, this commit therefore remove
> redundant preempt_disable/enable() in srcu_gp_start_if_needed()
> and adds a call to lockdep_assert_preemption_disabled() in order
> to enable lockdep to diagnose mistaken invocations of this function
> from preempts-enabled code.
> 
> Fixes: 65b4a59557f6 ("srcu: Make Tiny SRCU explicitly disable preemption")
> Signed-off-by: Zqiang <qiang.zhang@linux.dev>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

I replaced your v2 with this v3, thank you both!

							Thanx, Paul

> ---
>  kernel/rcu/srcutiny.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index b52ec45698e8..3450c3751ef7 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -181,10 +181,9 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
>  {
>  	unsigned long cookie;
>  
> -	preempt_disable();  // Needed for PREEMPT_LAZY
> +	lockdep_assert_preemption_disabled(); // Needed for PREEMPT_LAZY
>  	cookie = get_state_synchronize_srcu(ssp);
>  	if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) {
> -		preempt_enable();
>  		return;
>  	}
>  	WRITE_ONCE(ssp->srcu_idx_max, cookie);
> @@ -194,7 +193,6 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
>  		else if (list_empty(&ssp->srcu_work.entry))
>  			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
>  	}
> -	preempt_enable();
>  }
>  
>  /*
> -- 
> 2.48.1
>