linux-kernel - Re: BUG: spinlock trylock failure on UP, i.MX28 3.12.15-rt25

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Date:	Wed, 23 Apr 2014 09:14:33 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Stanislav Meduna <stano@...una.org>,
	"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: BUG: spinlock trylock failure on UP, i.MX28 3.12.15-rt25

On 04/22/2014 08:16 PM, Steven Rostedt wrote:
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -1447,6 +1447,12 @@ static void run_timer_softirq(struct softirq_action *h)
>  		__run_timers(base);
>  }
>  
> +#ifdef CONFIG_SMP
> +#define timer_should_raise_softirq(lock)	!spin_do_trylock(lock)
> +#else
> +#define timer_should_raise_softirq(lock)	1
> +#endif
> +

No. The lock may be taken but it also may be available no matter if UP
or not. With this patch applied the lockdep splat will go away but the
FULL_NO_HZ people will come back because the timer softirq is scheduled
even if no timer has expired.

Sebastian
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