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

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Date:	Sat, 14 Nov 2015 12:40:42 +0800
From:	yjin <yanjiang.jin@...driver.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	<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 2015年11月14日 12:25, Steven Rostedt wrote:
> On Sat, 14 Nov 2015 10:53:18 +0800
> <yanjiang.jin@...driver.com> wrote:
>
>> From: Yanjiang Jin <yanjiang.jin@...driver.com>
>>
>> This can only happen in RT kernel due to run_timer_softirq() calls
>> irq_work_tick() when CONFIG_PREEMPT_RT_FULL is enabled as below:
>>
>> static void run_timer_softirq(struct softirq_action *h)
>> {
>> ........
>> if defined(CONFIG_IRQ_WORK) && defined(CONFIG_PREEMPT_RT_FULL)
>>          irq_work_tick();
>> endif
>> ........
>> }
>>
>> Use raw_spin_{un,}lock_irq{save,restore} in push_irq_work_func() to
>> prevent following potentially deadlock scenario:
> Ug. No, the real fix is that the irq work is to be run from hard
> interrupt context.
But if so, we shouldn't call irq_work_tick() in run_timer_softirq(), right?

Thanks!
Yanjiang
> Moving the scheduling of high priority real-time
> tasks to ksoftirqd defeats the purpose. The question is, why is that
> irq work being run from thread context when it has the
> IRQ_WORK_HARD_IRQ flag set?
>
> -- Steve
>

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