Re: [RT PATCH] sched: rt: fix two possible deadlocks in push_irq_work_func

[Steven Rostedt]

On Sat, 14 Nov 2015 10:53:18 +0800
<yanjiang.jin@xxxxxxxxxxxxx> wrote:

> From: Yanjiang Jin <yanjiang.jin@xxxxxxxxxxxxx>
> 
> 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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