rcu: Use IRQ_WORK_INIT_HARD() to avoid rcu_read_unlock() hangs

When booting kernels built with both CONFIG_RCU_STRICT_GRACE_PERIOD=y
and CONFIG_PREEMPT_RT=y, the rcu_read_unlock_special() function's
invocation of irq_work_queue_on() the init_irq_work() causes the
rcu_preempt_deferred_qs_handler() function to work execute in SCHED_FIFO
irq_work kthreads.  Because rcu_read_unlock_special() is invoked on each
rcu_read_unlock() in such kernels, the amount of work just keeps piling
up, resulting in a boot-time hang.

This commit therefore avoids this hang by using IRQ_WORK_INIT_HARD()
instead of init_irq_work(), but only in kernels built with both
CONFIG_PREEMPT_RT=y and CONFIG_RCU_STRICT_GRACE_PERIOD=y.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 5c23aceecd62d2b311199c56c959d9348880918c..2a371541907306877ceb42b68457cb200f7d13e5 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -661,7 +661,13 @@ static void rcu_read_unlock_special(struct task_struct *t)
                            expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
                                // Get scheduler to re-evaluate and call hooks.
                                // If !IRQ_WORK, FQS scan will eventually IPI.
-                               init_irq_work(&rdp->defer_qs_iw, rcu_preempt_deferred_qs_handler);
+                               if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
+                                   IS_ENABLED(CONFIG_PREEMPT_RT))
+                                       rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(
+                                                               rcu_preempt_deferred_qs_handler);
+                               else
+                                       init_irq_work(&rdp->defer_qs_iw,
+                                                     rcu_preempt_deferred_qs_handler);
                                rdp->defer_qs_iw_pending = true;
                                irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
                        }