On Thu, Dec 09, 2021 at 03:09:30PM +0000, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
>
> 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.
And again, if testing goes well and you don't get it there first, I
expect to push this during the v5.18 merge window. In case you
would like to push this with the rest of this series:
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> ---
> kernel/rcu/tree.c | 1 +
> kernel/rcu/tree.h | 3 +++
> kernel/rcu/tree_plugin.h | 10 ++++++++--
> 3 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index a1bb0b1229ed..809855474b39 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4527,6 +4527,7 @@ 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);
> }
> }
>
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index aff4cc9303fb..055e30b3e5e0 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -108,6 +108,9 @@ 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. */
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 5199559fbbf0..3b4ee0933710 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1162,15 +1162,16 @@ 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;
> @@ -1178,6 +1179,9 @@ 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);
> }
>
> /*
> @@ -1200,6 +1204,7 @@ 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)
> @@ -1207,6 +1212,7 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
> if (cpumask_weight(cm) == 0)
> cpumask_setall(cm);
> set_cpus_allowed_ptr(t, cm);
> + mutex_unlock(&rnp->boost_kthread_mutex);
> free_cpumask_var(cm);
> }
>
> --
> 2.31.1
>
