On Fri, Feb 26, 2016 at 06:43:44PM -0000, Thomas Gleixner wrote:
> Make the RCU CPU_DYING_IDLE callback an explicit function call, so it gets
> invoked at the proper place.
>
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>
A question below...
> ---
> include/linux/cpu.h | 4 +---
> include/linux/notifier.h | 2 ++
> include/linux/rcupdate.h | 4 +---
> kernel/cpu.c | 1 +
> kernel/rcu/tree.c | 26 +++++++++++++++-----------
> kernel/sched/idle.c | 2 --
> 6 files changed, 20 insertions(+), 19 deletions(-)
>
> Index: b/include/linux/cpu.h
> ===================================================================
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -101,9 +101,7 @@ enum {
> * Called on the new cpu, just before
> * enabling interrupts. Must not sleep,
> * must not fail */
> -#define CPU_DYING_IDLE 0x000B /* CPU (unsigned)v dying, reached
> - * idle loop. */
> -#define CPU_BROKEN 0x000C /* CPU (unsigned)v did not die properly,
> +#define CPU_BROKEN 0x000B /* CPU (unsigned)v did not die properly,
> * perhaps due to preemption. */
>
> /* Used for CPU hotplug events occurring while tasks are frozen due to a
> suspend
> Index: b/include/linux/notifier.h
> ===================================================================
> --- a/include/linux/notifier.h
> +++ b/include/linux/notifier.h
> @@ -47,6 +47,8 @@
> * runtime initialization.
> */
>
> +struct notifier_block;
> +
> typedef int (*notifier_fn_t)(struct notifier_block *nb,
> unsigned long action, void *data);
>
> Index: b/include/linux/rcupdate.h
> ===================================================================
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -332,9 +332,7 @@ void rcu_init(void);
> void rcu_sched_qs(void);
> void rcu_bh_qs(void);
> void rcu_check_callbacks(int user);
> -struct notifier_block;
> -int rcu_cpu_notify(struct notifier_block *self,
> - unsigned long action, void *hcpu);
> +void rcu_report_dead(unsigned int cpu);
>
> #ifndef CONFIG_TINY_RCU
> void rcu_end_inkernel_boot(void);
> Index: b/kernel/cpu.c
> ===================================================================
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -762,6 +762,7 @@ void cpuhp_report_idle_dead(void)
> BUG_ON(st->state != CPUHP_AP_OFFLINE);
> st->state = CPUHP_AP_IDLE_DEAD;
> complete(&st->done);
What prevents the other CPU from killing this CPU at this point, so
that this CPU does not tell RCU that it is dead?
I agree that the odds should be low, but there are all manner of things
that might delay a CPU for just a little bit too long...
Or am I missing something subtle here?
Thanx, Paul
> + rcu_report_dead(smp_processor_id());
> }
>
> #else
> Index: b/kernel/rcu/tree.c
> ===================================================================
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4247,6 +4247,21 @@ static void rcu_prepare_cpu(int cpu)
> rcu_init_percpu_data(cpu, rsp);
> }
>
> +#ifdef CONFIG_HOTPLUG_CPU
> +void rcu_report_dead(unsigned int cpu)
> +{
> + struct rcu_state *rsp;
> +
> + /* QS for any half-done expedited RCU-sched GP. */
> + preempt_disable();
> + rcu_report_exp_rdp(&rcu_sched_state,
> + this_cpu_ptr(rcu_sched_state.rda), true);
> + preempt_enable();
> + for_each_rcu_flavor(rsp)
> + rcu_cleanup_dying_idle_cpu(cpu, rsp);
> +}
> +#endif
> +
> /*
> * Handle CPU online/offline notification events.
> */
> @@ -4278,17 +4293,6 @@ int rcu_cpu_notify(struct notifier_block
> for_each_rcu_flavor(rsp)
> rcu_cleanup_dying_cpu(rsp);
> break;
> - case CPU_DYING_IDLE:
> - /* QS for any half-done expedited RCU-sched GP. */
> - preempt_disable();
> - rcu_report_exp_rdp(&rcu_sched_state,
> - this_cpu_ptr(rcu_sched_state.rda), true);
> - preempt_enable();
> -
> - for_each_rcu_flavor(rsp) {
> - rcu_cleanup_dying_idle_cpu(cpu, rsp);
> - }
> - break;
> case CPU_DEAD:
> case CPU_DEAD_FROZEN:
> case CPU_UP_CANCELED:
> Index: b/kernel/sched/idle.c
> ===================================================================
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -220,8 +220,6 @@ static void cpu_idle_loop(void)
> rmb();
>
> if (cpu_is_offline(smp_processor_id())) {
> - rcu_cpu_notify(NULL, CPU_DYING_IDLE,
> - (void
> *)(long)smp_processor_id());
> cpuhp_report_idle_dead();
> arch_cpu_idle_dead();
> }
>
>
