When multiple CPUs in the same nocb gp/cb group concurrently
come online, they might try to concurrently create the same
rcuog kthread. Fix this by using nocb gp CPU's spawn mutex to
provide mutual exclusion for the rcuog kthread creation code.
Signed-off-by: Neeraj Upadhyay <[email protected]>
---
kernel/rcu/tree.h | 2 ++
kernel/rcu/tree_nocb.h | 3 +++
2 files changed, 5 insertions(+)
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 4b889081f4f4..9815b7844e58 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -204,6 +204,8 @@ struct rcu_data {
int nocb_defer_wakeup; /* Defer wakeup of nocb_kthread. */
struct timer_list nocb_timer; /* Enforce finite deferral. */
unsigned long nocb_gp_adv_time; /* Last call_rcu() CB adv (jiffies). */
+ struct mutex nocb_gp_kthread_mutex; /* Exclusion for nocb gp kthread */
+ /* spawning */
/* The following fields are used by call_rcu, hence own cacheline. */
raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp;
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index eeafb546a7a0..4f67e7d026b6 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1226,6 +1226,7 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
raw_spin_lock_init(&rdp->nocb_gp_lock);
timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
rcu_cblist_init(&rdp->nocb_bypass);
+ mutex_init(&rdp->nocb_gp_kthread_mutex);
}
/*
@@ -1248,6 +1249,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
/* If we didn't spawn the GP kthread first, reorganize! */
rdp_gp = rdp->nocb_gp_rdp;
+ mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
if (!rdp_gp->nocb_gp_kthread) {
t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
"rcuog/%d", rdp_gp->cpu);
@@ -1255,6 +1257,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
return;
WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
}
+ mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
/* Spawn the kthread for this CPU. */
t = kthread_run(rcu_nocb_cb_kthread, rdp,
--
2.17.1