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rcu: Add mutex for rcu boost kthread spawning and affinity setting

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As we handle parallel CPU bringup, we will need to take care to avoid
spawning multiple boost threads, or race conditions when setting their
affinity. Spotted by Paul McKenney.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
David Woodhouse 2021-12-08 23:41:53 +00:00 committed by Paul E. McKenney
parent 150154aae4
commit 218b957a69
3 changed files with 12 additions and 2 deletions
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1
kernel/rcu/tree.c
View File

@ -4570,6 +4570,7 @@ static void __init rcu_init_one(void)
init_waitqueue_head(&rnp->exp_wq[2]);
init_waitqueue_head(&rnp->exp_wq[3]);
spin_lock_init(&rnp->exp_lock);
mutex_init(&rnp->boost_kthread_mutex);
}
}

3
kernel/rcu/tree.h
View File

@ -110,6 +110,9 @@ struct rcu_node {
/* side effect, not as a lock. */
unsigned long boost_time;
/* When to start boosting (jiffies). */
struct mutex boost_kthread_mutex;
/* Exclusion for thread spawning and affinity */
/* manipulation. */
struct task_struct *boost_kthread_task;
/* kthread that takes care of priority */
/* boosting for this rcu_node structure. */

10
kernel/rcu/tree_plugin.h
View File

@ -1172,15 +1172,16 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
struct sched_param sp;
struct task_struct *t;
mutex_lock(&rnp->boost_kthread_mutex);
if (rnp->boost_kthread_task || !rcu_scheduler_fully_active)
return;
goto out;
rcu_state.boost = 1;
t = kthread_create(rcu_boost_kthread, (void *)rnp,
"rcub/%d", rnp_index);
if (WARN_ON_ONCE(IS_ERR(t)))
return;
goto out;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->boost_kthread_task = t;
@ -1188,6 +1189,9 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
out:
mutex_unlock(&rnp->boost_kthread_mutex);
}
/*
@ -1210,6 +1214,7 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
return;
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
return;
mutex_lock(&rnp->boost_kthread_mutex);
for_each_leaf_node_possible_cpu(rnp, cpu)
if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
cpu != outgoingcpu)
@ -1218,6 +1223,7 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
if (cpumask_weight(cm) == 0)
cpumask_copy(cm, housekeeping_cpumask(HK_FLAG_RCU));
set_cpus_allowed_ptr(t, cm);
mutex_unlock(&rnp->boost_kthread_mutex);
free_cpumask_var(cm);
}