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

Frederic Weisbecker
2023-12-08T22:06:04Z

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>
---
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