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

Paul E. McKenney
2025-09-10T15:52:21Z

On Wed, Sep 10, 2025 at 10:36:20AM -0400, Joel Fernandes wrote:
> [..]
> > > 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();
>
> nit: Do we still want to keep the comment that the expectation of preemption
> being disabled is for the LAZY case?

Good point, and I do believe that we do. Zqiang, any reason not to
add this comment back in?

Thanx, Paul

> thanks,
>
> - Joel
>
>
> > > 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
> > >