linux-kernel - Re: [PATCH] softirq: add irq off checking for __raise_softirq

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Message-ID: <20200813055822.GC3982@worktop.programming.kicks-ass.net>
Date:   Thu, 13 Aug 2020 07:58:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiafei Pan <Jiafei.Pan@....com>
Cc:     mingo@...nel.org, tglx@...utronix.de, rostedt@...dmis.org,
        romain.perier@...il.com, will@...nel.org,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        leoyang.li@....com, vladimir.oltean@....com
Subject: Re: [PATCH] softirq: add irq off checking for __raise_softirq_irqoff

On Thu, Aug 06, 2020 at 12:07:29PM +0800, Jiafei Pan wrote:
> __raise_softirq_irqoff will update per-CPU mask of pending softirqs,
> it need to be called in irq disabled context in order to keep it atomic
> operation, otherwise it will be interrupted by hardware interrupt,
> and per-CPU softirqs pending mask will be corrupted, the result is
> there will be unexpected issue, for example hrtimer soft irq will
> be losed and soft hrtimer will never be expire and handled.
> 
> Adding irqs disabled checking here to provide warning in irqs enabled
> context.
> 
> Signed-off-by: Jiafei Pan <Jiafei.Pan@....com>
> ---
>  kernel/softirq.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index bf88d7f62433..11f61e54a3ae 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -481,6 +481,11 @@ void raise_softirq(unsigned int nr)
>  
>  void __raise_softirq_irqoff(unsigned int nr)
>  {
> +	/* This function can only be called in irq disabled context,
> +	 * otherwise or_softirq_pending will be interrupted by hardware
> +	 * interrupt, so that there will be unexpected issue.
> +	 */

Comment style is wrong, also I'm not sure the comment is really
helpfull.

> +	WARN_ON_ONCE(!irqs_disabled());

	lockdep_assert_irqs_disabled();

>  	trace_softirq_raise(nr);
>  	or_softirq_pending(1UL << nr);
>  }