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

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Message-ID: <20151113232512.53df431f@gandalf.local.home>
Date:	Fri, 13 Nov 2015 23:25:12 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	<yanjiang.jin@...driver.com>
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 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. 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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