>
> Signed-off-by: Joel Fernandes <[email protected]>
>
> ---
>
> kernel/rcu/tree.h | 11 ++++++++++-
>
> kernel/rcu/tree_plugin.h | 29 ++++++++++++++++++++++-------
>
> 2 files changed, 32 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
>
> index 3830c19cf2f6..f8f612269e6e 100644
>
> --- a/kernel/rcu/tree.h
>
> +++ b/kernel/rcu/tree.h
>
> @@ -174,6 +174,15 @@ struct rcu_snap_record {
>
> unsigned long jiffies; /* Track jiffies value */
>
> };
>
>
>
> +/*
>
> + * The IRQ work (deferred_qs_iw) is used by RCU to get scheduler's attention.
>
> + * It can be in one of the following states:
>
> + * - DEFER_QS_IDLE: An IRQ work was never scheduled.
>
> + * - DEFER_QS_PENDING: An IRQ work was scheduler but never run.
>
> + */
>
> +#define DEFER_QS_IDLE 0
>
> +#define DEFER_QS_PENDING 1
>
> +
>
> /* Per-CPU data for read-copy update. */
>
> struct rcu_data {
>
> /* 1) quiescent-state and grace-period handling : */
>
> @@ -192,7 +201,7 @@ struct rcu_data {
>
> /* during and after the last grace */
>
> /* period it is aware of. */
>
> struct irq_work defer_qs_iw; /* Obtain later scheduler attention. */
>
> - bool defer_qs_iw_pending; /* Scheduler attention pending? */
>
> + int defer_qs_iw_pending; /* Scheduler attention pending? */
>
> struct work_struct strict_work; /* Schedule readers for strict GPs. */
>
>
>
> /* 2) batch handling */
>
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
>
> index dd1c156c1759..baf57745b42f 100644
>
> --- a/kernel/rcu/tree_plugin.h
>
> +++ b/kernel/rcu/tree_plugin.h
>
> @@ -486,13 +486,16 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct
> *t, unsigned long flags)
>
> struct rcu_node *rnp;
>
> union rcu_special special;
>
>
>
> + rdp = this_cpu_ptr(&rcu_data);
>
> + if (rdp->defer_qs_iw_pending == DEFER_QS_PENDING)
>
> + rdp->defer_qs_iw_pending = DEFER_QS_IDLE;
>
> +
>
> /*
>
> * If RCU core is waiting for this CPU to exit its critical section,
>
> * report the fact that it has exited. Because irqs are disabled,
>
> * t->rcu_read_unlock_special cannot change.
>
> */
>
> special = t->rcu_read_unlock_special;
>
> - rdp = this_cpu_ptr(&rcu_data);
>
> if (!special.s && !rdp->cpu_no_qs.b.exp) {
>
> local_irq_restore(flags);
>
> return;
>
> @@ -623,12 +626,24 @@ notrace void rcu_preempt_deferred_qs(struct task_struct
> *t)
>
> */
>
> static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
>
> {
>
> - unsigned long flags;
>
> - struct rcu_data *rdp;
>
> + volatile unsigned long flags;
>
> + struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
>
>
>
> - rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
>
> local_irq_save(flags);
>
> - rdp->defer_qs_iw_pending = false;
>
> +
>
> + /*
>
> + * Requeue the IRQ work on next unlock in following situation:
>
> + * 1. rcu_read_unlock() queues IRQ work (state -> DEFER_QS_PENDING)
>
> + * 2. CPU enters new rcu_read_lock()
>
> + * 3. IRQ work runs but cannot report QS due to rcu_preempt_depth() > 0
>
> + * 4. rcu_read_unlock() does not re-queue work (state still PENDING)
>
> + * 5. Deferred QS reporting does not happen.
>
> + */
>
> + if (rcu_preempt_depth() > 0) {
For Preempt-RT kernels, the rcu_preempt_deferred_qs_handler() be invoked
in per-cpu irq_work kthreads, the return value of rcu_preempt_depth()
may always be 0, should we use IRQ_WORK_INIT_HARD() to initialize defer_qs_iw?
Thanks
Zqiang
>
> + WRITE_ONCE(rdp->defer_qs_iw_pending, DEFER_QS_IDLE);
>
> + local_irq_restore(flags);
>
> + return;
>
> + }
>
> local_irq_restore(flags);
>
> }
>
>
>
> @@ -675,7 +690,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
>
> set_tsk_need_resched(current);
>
> set_preempt_need_resched();
>
> if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
>
> - expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
>
> + expboost && rdp->defer_qs_iw_pending != DEFER_QS_PENDING &&
> cpu_online(rdp->cpu)) {
>
> // Get scheduler to re-evaluate and call hooks.
>
> // If !IRQ_WORK, FQS scan will eventually IPI.
>
> if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
>
> @@ -685,7 +700,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
>
> else
>
> init_irq_work(&rdp->defer_qs_iw,
>
> rcu_preempt_deferred_qs_handler);
>
> - rdp->defer_qs_iw_pending = true;
>
> + rdp->defer_qs_iw_pending = DEFER_QS_PENDING;
>
> irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
>
> }
>
> }
>
> --
>
> 2.43.0
>
