Re: [PATCH RFC v2 rcu 2/8] srcu: Create an srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe()

Frederic Weisbecker
2022-10-02T15:55:29Z

On Thu, Sep 29, 2022 at 11:07:25AM -0700, Paul E. McKenney wrote:
> @@ -1090,7 +1121,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
> int ss_state;
>
> check_init_srcu_struct(ssp);
> - idx = srcu_read_lock(ssp);
> + idx = __srcu_read_lock_nmisafe(ssp);

Why do we need to force the atomic based version here (even if CONFIG_NEED_SRCU_NMI_SAFE=y)?

> ss_state = smp_load_acquire(&ssp->srcu_size_state);
> if (ss_state < SRCU_SIZE_WAIT_CALL)
> sdp = per_cpu_ptr(ssp->sda, 0);
> @@ -1123,7 +1154,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
> srcu_funnel_gp_start(ssp, sdp, s, do_norm);
> else if (needexp)
> srcu_funnel_exp_start(ssp, sdp_mynode, s);
> - srcu_read_unlock(ssp, idx);
> + __srcu_read_unlock_nmisafe(ssp, idx);
> return s;
> }
>
> @@ -1427,13 +1458,13 @@ void srcu_barrier(struct srcu_struct *ssp)
> /* Initial count prevents reaching zero until all CBs are posted. */
> atomic_set(&ssp->srcu_barrier_cpu_cnt, 1);
>
> - idx = srcu_read_lock(ssp);
> + idx = __srcu_read_lock_nmisafe(ssp);

And same here?

Thanks.

> if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
> srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0));
> else
> for_each_possible_cpu(cpu)
> srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu));
> - srcu_read_unlock(ssp, idx);
> + __srcu_read_unlock_nmisafe(ssp, idx);
>
> /* Remove the initial count, at which point reaching zero can happen. */
> if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))
> --
> 2.31.1.189.g2e36527f23
>