linux-kernel - Re: [RT PATCH] sched: rt: fix two possible deadlocks in push_irq_work

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Date:	Sun, 15 Nov 2015 12:05:51 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	yjin <yanjiang.jin@...driver.com>
cc:	Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
	bigeasy@...utronix.de, peterz@...radead.org,
	linux-kernel@...r.kernel.org, jinyanjiang@...il.com,
	stable-rt@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [RT PATCH] sched: rt: fix two possible deadlocks in
 push_irq_work_func

On Sun, 15 Nov 2015, Thomas Gleixner wrote:
> Which does not happen on MIPS as it uses the generic
> arch_irq_work_has_interrupt() implementation which returns 'false'.

So the proper fix is to ensure that the irq safe irq work actually
happens in interrupt context. Patch below.

Thanks,

	tglx

8<-------------

diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index 0e427a9997f3..2543aab05daa 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -52,4 +52,10 @@ static inline bool irq_work_needs_cpu(void) { return false; }
 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 */
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 5a0f4525139c..58cf46638ca0 100644
--- 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
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index adb1d82d6631..c68ba873da3c 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1455,7 +1455,7 @@ 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
@@ -1471,9 +1471,7 @@ static void run_timer_softirq(struct softirq_action *h)
 
 	hrtimer_run_pending();
 
-#if defined(CONFIG_IRQ_WORK) && defined(CONFIG_PREEMPT_RT_FULL)
-	irq_work_tick();
-#endif
+	irq_work_tick_soft();
 
 	if (time_after_eq(jiffies, base->timer_jiffies))
 		__run_timers(base);
--
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