Re: [PATCH v3 3/4] rcu/nocb: Protect NOCB state via local_lock() under PREEMPT_RT
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: 2021-08-17 15:36:21
Also in:
linux-rt-users, lkml, rcu
On 2021-08-11 21:13:53 [+0100], Valentin Schneider wrote:
quoted hunk ↗ jump to hunk
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 0ff5e4fb933e..11c4ff00afde 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h@@ -21,6 +21,17 @@ static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp) return lockdep_is_held(&rdp->nocb_lock); } +static inline int rcu_lockdep_is_held_nocb_local(struct rcu_data *rdp) +{ + return lockdep_is_held( +#ifdef CONFIG_PREEMPT_RT + &rdp->nocb_local_lock.lock +#else + &rdp->nocb_local_lock +#endif + ); +}
Now that I see it and Paul asked for it, please just use !RT version. return lockdep_is_held(&rdp->nocb_local_lock); and RT will work, too.
quoted hunk ↗ jump to hunk
static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) { /* Race on early boot between thread creation and assignment */@@ -1629,6 +1664,22 @@ static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, } } +/* + * The invocation of rcu_core() within the RCU core kthreads remains preemptible + * under PREEMPT_RT, thus the offload state of a CPU could change while + * said kthreads are preempted. Prevent this from happening by protecting the + * offload state with a local_lock(). + */ +static void rcu_nocb_local_lock(struct rcu_data *rdp) +{ + local_lock(&rcu_data.nocb_local_lock); +} + +static void rcu_nocb_local_unlock(struct rcu_data *rdp) +{ + local_unlock(&rcu_data.nocb_local_lock); +} +
Do you need to pass rdp given that it is not used?
/* Lockdep check that ->cblist may be safely accessed. */
static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
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