linux-kernel - Re: [PATCH] irq_poll: Use raise_softirq_irqoff() in cpu

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Date:   Mon, 18 Oct 2021 09:45:47 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] irq_poll: Use raise_softirq_irqoff() in cpu_dead notifier

On 2021-09-30 12:37:54 [+0200], To linux-kernel@...r.kernel.org wrote:
> __raise_softirq_irqoff() adds a bit to the pending sofirq mask and this
> is it. The softirq won't be handled in a deterministic way but randomly
> when an interrupt fires and handles softirq in its irq_exit() routine or
> if something randomly checks and handles pending softirqs in the call
> chain before the CPU goes idle.
> 
> Add a local_bh_disable/enable() around the IRQ-off section which will
> handle pending softirqs.

ping

> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  lib/irq_poll.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/lib/irq_poll.c b/lib/irq_poll.c
> index 2f17b488d58e1..2b9f797642f60 100644
> --- a/lib/irq_poll.c
> +++ b/lib/irq_poll.c
> @@ -191,11 +191,13 @@ static int irq_poll_cpu_dead(unsigned int cpu)
>  	 * If a CPU goes away, splice its entries to the current CPU
>  	 * and trigger a run of the softirq
>  	 */
> +	local_bh_disable();
>  	local_irq_disable();
>  	list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
>  			 this_cpu_ptr(&blk_cpu_iopoll));
>  	__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
>  	local_irq_enable();
> +	local_bh_enable();
>  
>  	return 0;
>  }
> -- 
> 2.33.0
> 

Sebastian