Subject: irqwork: Move irq safe work to irq context
From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 15 Nov 2015 18:40:17 +0100

On architectures where arch_irq_work_has_interrupt() returns false, we
end up running the irq safe work from the softirq context. That
results in a potential deadlock in the scheduler irq work which
expects that function to be called with interrupts disabled.

Split the irq_work_tick() function into a hard and soft variant. Call
the hard variant from the tick interrupt and add the soft variant to
the timer softirq.

Reported-and-tested-by: Yanjiang Jin <yanjiang.jin@windriver.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
---
 include/linux/irq_work.h |    6 ++++++
 kernel/irq_work.c        |    9 +++++++++
 kernel/time/timer.c      |    6 ++----
 3 files changed, 17 insertions(+), 4 deletions(-)

--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -52,4 +52,10 @@ static inline bool irq_work_needs_cpu(vo
 static inline void irq_work_run(void) { }
 #endif
 
+#if defined(CONFIG_IRQ_WORK) && defined(CONFIG_PREEMPT_RT_FULL)
+void irq_work_tick_soft(void);
+#else
+static inline void irq_work_tick_soft(void) { }
+#endif
+
 #endif /* _LINUX_IRQ_WORK_H */
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -200,8 +200,17 @@ void irq_work_tick(void)
 
 	if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
 		irq_work_run_list(raised);
+
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT_FULL))
+		irq_work_run_list(this_cpu_ptr(&lazy_list));
+}
+
+#if defined(CONFIG_IRQ_WORK) && defined(CONFIG_PREEMPT_RT_FULL)
+void irq_work_tick_soft(void)
+{
 	irq_work_run_list(this_cpu_ptr(&lazy_list));
 }
+#endif
 
 /*
  * Synchronize against the irq_work @entry, ensures the entry is not
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1604,7 +1604,7 @@ void update_process_times(int user_tick)
 	scheduler_tick();
 	run_local_timers();
 	rcu_check_callbacks(user_tick);
-#if defined(CONFIG_IRQ_WORK) && !defined(CONFIG_PREEMPT_RT_FULL)
+#if defined(CONFIG_IRQ_WORK)
 	if (in_irq())
 		irq_work_tick();
 #endif
@@ -1645,9 +1645,7 @@ static __latent_entropy void run_timer_s
 {
 	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
 
-#if defined(CONFIG_IRQ_WORK) && defined(CONFIG_PREEMPT_RT_FULL)
-	irq_work_tick();
-#endif
+	irq_work_tick_soft();
 
 	__run_timers(base);
 	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active)