Re: [PATCH 4/8] rcu/exp: Handle RCU expedited grace period kworker allocation failure

Kalesh Singh
2023-12-12T16:14:49Z

On Fri, Dec 8, 2023 at 5:06 PM Frederic Weisbecker <frederic@kernel.org> wrote:
>
> Just like is done for the kworker performing nodes initialization,
> gracefully handle the possible allocation failure of the RCU expedited
> grace period main kworker.
>
> While at it perform a rename of the related checking functions to better
> reflect the expedited specifics.
>
> Fixes: 9621fbee44df ("rcu: Move expedited grace period (GP) work to RT kthread_worker")
> Cc: Kalesh Singh <kaleshsingh@google.com>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Reviewed-by: Kalesh Singh <kaleshsingh@google.com>

Thanks,
Kalesh

> ---
> kernel/rcu/tree.c | 2 ++
> kernel/rcu/tree_exp.h | 25 +++++++++++++++++++------
> 2 files changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 055f4817bc70..39679cf66c3a 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4717,6 +4717,7 @@ static void __init rcu_start_exp_gp_kworkers(void)
> rcu_exp_gp_kworker = kthread_create_worker(0, gp_kworker_name);
> if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
> pr_err("Failed to create %s!\n", gp_kworker_name);
> + rcu_exp_gp_kworker = NULL;
> return;
> }
>
> @@ -4725,6 +4726,7 @@ static void __init rcu_start_exp_gp_kworkers(void)
> pr_err("Failed to create %s!\n", par_gp_kworker_name);
> rcu_exp_par_gp_kworker = NULL;
> kthread_destroy_worker(rcu_exp_gp_kworker);
> + rcu_exp_gp_kworker = NULL;
> return;
> }
>
> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> index 6d7cea5d591f..cb31f4fb4b36 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -429,7 +429,12 @@ static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
> __sync_rcu_exp_select_node_cpus(rewp);
> }
>
> -static inline bool rcu_gp_par_worker_started(void)
> +static inline bool rcu_exp_worker_started(void)
> +{
> + return !!READ_ONCE(rcu_exp_gp_kworker);
> +}
> +
> +static inline bool rcu_exp_par_worker_started(void)
> {
> return !!READ_ONCE(rcu_exp_par_gp_kworker);
> }
> @@ -479,7 +484,12 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
> __sync_rcu_exp_select_node_cpus(rewp);
> }
>
> -static inline bool rcu_gp_par_worker_started(void)
> +static inline bool rcu_exp_worker_started(void)
> +{
> + return !!READ_ONCE(rcu_gp_wq);
> +}
> +
> +static inline bool rcu_exp_par_worker_started(void)
> {
> return !!READ_ONCE(rcu_par_gp_wq);
> }
> @@ -542,7 +552,7 @@ static void sync_rcu_exp_select_cpus(void)
> rnp->exp_need_flush = false;
> if (!READ_ONCE(rnp->expmask))
> continue; /* Avoid early boot non-existent wq. */
> - if (!rcu_gp_par_worker_started() ||
> + if (!rcu_exp_par_worker_started() ||
> rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
> rcu_is_last_leaf_node(rnp)) {
> /* No worker started yet or last leaf, do direct call. */
> @@ -957,7 +967,7 @@ static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
> */
> void synchronize_rcu_expedited(void)
> {
> - bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
> + bool can_queue;
> unsigned long flags;
> struct rcu_exp_work rew;
> struct rcu_node *rnp;
> @@ -968,6 +978,9 @@ void synchronize_rcu_expedited(void)
> lock_is_held(&rcu_sched_lock_map),
> "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
>
> + can_queue = (rcu_scheduler_active != RCU_SCHEDULER_INIT) &&
> + rcu_exp_worker_started();
> +
> /* Is the state is such that the call is a grace period? */
> if (rcu_blocking_is_gp()) {
> // Note well that this code runs with !PREEMPT && !SMP.
> @@ -997,7 +1010,7 @@ void synchronize_rcu_expedited(void)
> return; /* Someone else did our work for us. */
>
> /* Ensure that load happens before action based on it. */
> - if (unlikely(boottime)) {
> + if (unlikely(!can_queue)) {
> /* Direct call during scheduler init and early_initcalls(). */
> rcu_exp_sel_wait_wake(s);
> } else {
> @@ -1015,7 +1028,7 @@ void synchronize_rcu_expedited(void)
> /* Let the next expedited grace period start. */
> mutex_unlock(&rcu_state.exp_mutex);
>
> - if (likely(!boottime))
> + if (likely(can_queue))
> synchronize_rcu_expedited_destroy_work(&rew);
> }
> EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
> --
> 2.42.1
>