Re: [PATCH v2] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if_needed()

Paul E. McKenney
2025-09-10T13:55:49Z

On Tue, Sep 09, 2025 at 09:39:28PM +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>

Very good, applied for testing and further review, thank you!

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..b2da188133fc 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();
> 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
>