Re: [PATCH 16/36] rcu: Fix rcu_idle_exit()

Mark Rutland
2022-06-14T16:14:57Z

On Wed, Jun 08, 2022 at 04:27:39PM +0200, Peter Zijlstra wrote:
> Current rcu_idle_exit() is terminally broken because it uses
> local_irq_{save,restore}(), which are traced which uses RCU.
>
> However, now that all the callers are sure to have IRQs disabled, we
> can remove these calls.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Acked-by: Paul E. McKenney <paulmck@kernel.org>

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
> kernel/rcu/tree.c | 9 +++------
> 1 file changed, 3 insertions(+), 6 deletions(-)
>
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -659,7 +659,7 @@ static noinstr void rcu_eqs_enter(bool u
> * If you add or remove a call to rcu_idle_enter(), be sure to test with
> * CONFIG_RCU_EQS_DEBUG=y.
> */
> -void rcu_idle_enter(void)
> +void noinstr rcu_idle_enter(void)
> {
> lockdep_assert_irqs_disabled();
> rcu_eqs_enter(false);
> @@ -896,13 +896,10 @@ static void noinstr rcu_eqs_exit(bool us
> * If you add or remove a call to rcu_idle_exit(), be sure to test with
> * CONFIG_RCU_EQS_DEBUG=y.
> */
> -void rcu_idle_exit(void)
> +void noinstr rcu_idle_exit(void)
> {
> - unsigned long flags;
> -
> - local_irq_save(flags);
> + lockdep_assert_irqs_disabled();
> rcu_eqs_exit(false);
> - local_irq_restore(flags);
> }
> EXPORT_SYMBOL_GPL(rcu_idle_exit);
>
>
>