rcu: permit rcu_read_unlock() to be called while holding runqueue locks
Avoid calling into the scheduler while holding core RCU locks. This
allows rcu_read_unlock() to be called while holding the runqueue locks,
but only as long as there was no chance of the RCU read-side critical
section having been preempted. (Otherwise, if RCU priority boosting
is enabled, rcu_read_unlock() might call into the scheduler in order to
unboost itself, which might allows self-deadlock on the runqueue locks
within the scheduler.)
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f629479..ed339702 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -711,15 +711,17 @@
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
+ unsigned long flags;
int must_wait = 0;
- raw_spin_lock(&rnp->lock); /* irqs already disabled */
- if (!list_empty(&rnp->blkd_tasks)) {
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ if (list_empty(&rnp->blkd_tasks))
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ else {
rnp->exp_tasks = rnp->blkd_tasks.next;
- rcu_initiate_boost(rnp);
+ rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
must_wait = 1;
}
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
if (!must_wait)
rcu_report_exp_rnp(rsp, rnp);
}
@@ -1179,12 +1181,7 @@
*/
static void rcu_boost_kthread_timer(unsigned long arg)
{
- unsigned long flags;
- struct rcu_node *rnp = (struct rcu_node *)arg;
-
- raw_spin_lock_irqsave(&rnp->lock, flags);
- invoke_rcu_node_kthread(rnp);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ invoke_rcu_node_kthread((struct rcu_node *)arg);
}
/*
@@ -1200,10 +1197,7 @@
for (;;) {
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
wait_event_interruptible(rnp->boost_wq, rnp->boost_tasks ||
- rnp->exp_tasks ||
- kthread_should_stop());
- if (kthread_should_stop())
- break;
+ rnp->exp_tasks);
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
more2boost = rcu_boost(rnp);
if (more2boost)
@@ -1215,7 +1209,7 @@
spincnt = 0;
}
}
- rnp->boost_kthread_status = RCU_KTHREAD_STOPPED;
+ /* NOTREACHED */
return 0;
}
@@ -1225,14 +1219,17 @@
* kthread to start boosting them. If there is an expedited grace
* period in progress, it is always time to boost.
*
- * The caller must hold rnp->lock.
+ * The caller must hold rnp->lock, which this function releases,
+ * but irqs remain disabled. The ->boost_kthread_task is immortal,
+ * so we don't need to worry about it going away.
*/
-static void rcu_initiate_boost(struct rcu_node *rnp)
+static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
{
struct task_struct *t;
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
rnp->n_balk_exp_gp_tasks++;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
if (rnp->exp_tasks != NULL ||
@@ -1242,11 +1239,14 @@
ULONG_CMP_GE(jiffies, rnp->boost_time))) {
if (rnp->exp_tasks == NULL)
rnp->boost_tasks = rnp->gp_tasks;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
t = rnp->boost_kthread_task;
if (t != NULL)
wake_up_process(t);
- } else
+ } else {
rcu_initiate_boost_trace(rnp);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ }
}
/*
@@ -1312,27 +1312,11 @@
return 0;
}
-#ifdef CONFIG_HOTPLUG_CPU
-
-static void rcu_stop_boost_kthread(struct rcu_node *rnp)
-{
- unsigned long flags;
- struct task_struct *t;
-
- raw_spin_lock_irqsave(&rnp->lock, flags);
- t = rnp->boost_kthread_task;
- rnp->boost_kthread_task = NULL;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- if (t != NULL)
- kthread_stop(t);
-}
-
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
-
#else /* #ifdef CONFIG_RCU_BOOST */
-static void rcu_initiate_boost(struct rcu_node *rnp)
+static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
{
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
@@ -1355,14 +1339,6 @@
return 0;
}
-#ifdef CONFIG_HOTPLUG_CPU
-
-static void rcu_stop_boost_kthread(struct rcu_node *rnp)
-{
-}
-
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
-
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifndef CONFIG_SMP